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 $183.73   5.668%   $194.1438   $194.14   $194.15   $194.10  
  Purchase #2 $96.51   10.371%   $106.5191   $106.52   $106.50   $106.50  
  Purchase #3 $209.28   11.180%   $232.6775   $232.68   $232.70   $232.70  
  Purchase #4 $210.44   12.414%   $236.564   $236.56   $236.55   $236.60  
  Purchase #5 $169.99   7.616%   $182.9364   $182.94   $182.95   $182.90  
  Purchase #6 $87.60   8.237%   $94.8156   $94.82   $94.80   $94.80  
  Purchase #7 $246.67   11.758%   $275.6735   $275.67   $275.65   $275.70  
  7 purchase totals = $1,204.22       $1,323.3299   $1,323.33   $1,323.30   $1,323.30