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 $106.69   11.252%   $118.6948   $118.69   $118.70   $118.70  
  Purchase #2 $24.83   12.845%   $28.0194   $28.02   $28.00   $28.00  
  Purchase #3 $190.79   3.571%   $197.6031   $197.60   $197.60   $197.60  
  Purchase #4 $87.52   11.722%   $97.7791   $97.78   $97.80   $97.80  
  Purchase #5 $54.35   12.627%   $61.2128   $61.21   $61.20   $61.20  
  Purchase #6 $117.67   5.611%   $124.2725   $124.27   $124.25   $124.30  
  Purchase #7 $211.32   6.679%   $225.4341   $225.43   $225.45   $225.40  
  7 purchase totals = $793.17       $853.0158   $853.00   $853.00   $853.00