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 $56.30   3.659%   $58.36   $58.36   $58.35   $58.40  
  Purchase #2 $129.95   13.368%   $147.3217   $147.32   $147.30   $147.30  
  Purchase #3 $58.94   3.504%   $61.0053   $61.01   $61.00   $61.00  
  Purchase #4 $57.78   3.774%   $59.9606   $59.96   $59.95   $60.00  
  Purchase #5 $201.47   3.196%   $207.909   $207.91   $207.90   $207.90  
  Purchase #6 $206.88   10.131%   $227.839   $227.84   $227.85   $227.80  
  Purchase #7 $241.69   5.638%   $255.3165   $255.32   $255.30   $255.30  
  7 purchase totals = $953.01       $1,017.7121   $1,017.72   $1,017.65   $1,017.70