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 $30.45   11.497%   $33.9508   $33.95   $33.95   $34.00  
  Purchase #2 $142.28   7.140%   $152.4388   $152.44   $152.45   $152.40  
  Purchase #3 $51.34   11.601%   $57.296   $57.30   $57.30   $57.30  
  Purchase #4 $209.36   4.505%   $218.7917   $218.79   $218.80   $218.80  
  Purchase #5 $205.40   11.107%   $228.2138   $228.21   $228.20   $228.20  
  Purchase #6 $216.83   5.603%   $228.979   $228.98   $229.00   $229.00  
  Purchase #7 $42.91   5.554%   $45.2932   $45.29   $45.30   $45.30  
  7 purchase totals = $898.57       $964.9633   $964.96   $965.00   $965.00