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 $210.99   11.547%   $235.353   $235.35   $235.35   $235.40  
  Purchase #2 $75.96   7.425%   $81.6   $81.60   $81.60   $81.60  
  Purchase #3 $58.96   9.510%   $64.5671   $64.57   $64.55   $64.60  
  Purchase #4 $144.45   4.871%   $151.4862   $151.49   $151.50   $151.50  
  Purchase #5 $45.38   12.112%   $50.8764   $50.88   $50.90   $50.90  
  Purchase #6 $248.36   13.385%   $281.603   $281.60   $281.60   $281.60  
  Purchase #7 $77.54   10.861%   $85.9616   $85.96   $85.95   $86.00  
  7 purchase totals = $861.64       $951.4473   $951.45   $951.45   $951.60