Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $232.25   9.496%   $254.3045   $254.30   $254.30   $254.30  
  Purchase #2 $145.43   7.622%   $156.5147   $156.51   $156.50   $156.50  
  Purchase #3 $111.99   11.325%   $124.6729   $124.67   $124.65   $124.70  
  Purchase #4 $93.51   12.547%   $105.2427   $105.24   $105.25   $105.20  
  Purchase #5 $129.30   8.793%   $140.6693   $140.67   $140.65   $140.70  
  Purchase #6 $212.57   5.387%   $224.0211   $224.02   $224.00   $224.00  
  Purchase #7 $219.84   13.641%   $249.8284   $249.83   $249.85   $249.80  
  7 purchase totals = $1,144.89       $1,255.2536   $1,255.24   $1,255.20   $1,255.20