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 $241.84   11.201%   $268.9285   $268.93   $268.95   $268.90  
  Purchase #2 $70.85   7.758%   $76.3465   $76.35   $76.35   $76.30  
  Purchase #3 $120.31   13.299%   $136.31   $136.31   $136.30   $136.30  
  Purchase #4 $24.94   3.498%   $25.8124   $25.81   $25.80   $25.80  
  Purchase #5 $173.93   13.219%   $196.9218   $196.92   $196.90   $196.90  
  Purchase #6 $91.60   10.294%   $101.0293   $101.03   $101.05   $101.00  
  Purchase #7 $60.65   12.302%   $68.1112   $68.11   $68.10   $68.10  
  7 purchase totals = $784.12       $873.4597   $873.46   $873.45   $873.30