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 $201.36   5.290%   $212.0119   $212.01   $212.00   $212.00  
  Purchase #2 $99.97   6.311%   $106.2791   $106.28   $106.30   $106.30  
  Purchase #3 $213.97   5.738%   $226.2476   $226.25   $226.25   $226.20  
  Purchase #4 $18.45   13.756%   $20.988   $20.99   $21.00   $21.00  
  Purchase #5 $145.32   5.690%   $153.5887   $153.59   $153.60   $153.60  
  Purchase #6 $203.53   11.782%   $227.5099   $227.51   $227.50   $227.50  
  Purchase #7 $74.35   3.460%   $76.9225   $76.92   $76.90   $76.90  
  7 purchase totals = $956.95       $1,023.5477   $1,023.55   $1,023.55   $1,023.50