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 $52.49   7.224%   $56.2819   $56.28   $56.30   $56.30  
  Purchase #2 $207.97   10.348%   $229.4907   $229.49   $229.50   $229.50  
  Purchase #3 $6.34   7.119%   $6.7913   $6.79   $6.80   $6.80  
  Purchase #4 $158.71   5.290%   $167.1058   $167.11   $167.10   $167.10  
  Purchase #5 $49.52   9.623%   $54.2853   $54.29   $54.30   $54.30  
  Purchase #6 $147.67   8.232%   $159.8262   $159.83   $159.85   $159.80  
  Purchase #7 $169.47   7.790%   $182.6717   $182.67   $182.65   $182.70  
  7 purchase totals = $792.17       $856.4529   $856.46   $856.50   $856.50