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 $40.31   7.158%   $43.1954   $43.20   $43.20   $43.20  
  Purchase #2 $132.60   9.541%   $145.2514   $145.25   $145.25   $145.30  
  Purchase #3 $158.89   5.194%   $167.1427   $167.14   $167.15   $167.10  
  Purchase #4 $60.80   6.846%   $64.9624   $64.96   $64.95   $65.00  
  Purchase #5 $195.72   10.119%   $215.5249   $215.52   $215.50   $215.50  
  Purchase #6 $69.36   8.160%   $75.0198   $75.02   $75.00   $75.00  
  Purchase #7 $48.30   7.852%   $52.0925   $52.09   $52.10   $52.10  
  7 purchase totals = $705.98       $763.1891   $763.18   $763.15   $763.20