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 $24.60   10.629%   $27.2147   $27.21   $27.20   $27.20  
  Purchase #2 $175.64   4.102%   $182.8448   $182.84   $182.85   $182.80  
  Purchase #3 $33.73   3.690%   $34.9746   $34.97   $34.95   $35.00  
  Purchase #4 $219.90   8.673%   $238.9719   $238.97   $238.95   $239.00  
  Purchase #5 $138.36   5.428%   $145.8702   $145.87   $145.85   $145.90  
  Purchase #6 $119.69   9.704%   $131.3047   $131.30   $131.30   $131.30  
  Purchase #7 $232.92   8.606%   $252.9651   $252.97   $252.95   $253.00  
  7 purchase totals = $944.84       $1,014.1460   $1,014.13   $1,014.05   $1,014.20