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 $51.86   11.270%   $57.7046   $57.70   $57.70   $57.70  
  Purchase #2 $219.97   11.582%   $245.4469   $245.45   $245.45   $245.40  
  Purchase #3 $24.36   10.843%   $27.0014   $27.00   $27.00   $27.00  
  Purchase #4 $241.93   12.520%   $272.2196   $272.22   $272.20   $272.20  
  Purchase #5 $133.53   9.421%   $146.1099   $146.11   $146.10   $146.10  
  Purchase #6 $77.81   10.692%   $86.1294   $86.13   $86.15   $86.10  
  Purchase #7 $18.48   5.766%   $19.5456   $19.55   $19.55   $19.50  
  7 purchase totals = $767.94       $854.1574   $854.16   $854.15   $854.00