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 $67.46   11.242%   $75.0439   $75.04   $75.05   $75.00  
  Purchase #2 $226.88   10.871%   $251.5441   $251.54   $251.55   $251.50  
  Purchase #3 $61.83   4.516%   $64.6222   $64.62   $64.60   $64.60  
  Purchase #4 $77.98   4.590%   $81.5593   $81.56   $81.55   $81.60  
  Purchase #5 $25.35   4.607%   $26.5179   $26.52   $26.50   $26.50  
  Purchase #6 $114.51   8.447%   $124.1827   $124.18   $124.20   $124.20  
  Purchase #7 $85.92   6.424%   $91.4395   $91.44   $91.45   $91.40  
  7 purchase totals = $659.93       $714.9096   $714.90   $714.90   $714.80