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 $87.45   10.137%   $96.3148   $96.31   $96.30   $96.30  
  Purchase #2 $26.35   12.598%   $29.6696   $29.67   $29.65   $29.70  
  Purchase #3 $125.94   11.867%   $140.8853   $140.89   $140.90   $140.90  
  Purchase #4 $91.67   3.343%   $94.7345   $94.73   $94.75   $94.70  
  Purchase #5 $87.45   6.303%   $92.962   $92.96   $92.95   $93.00  
  Purchase #6 $183.77   8.710%   $199.7764   $199.78   $199.80   $199.80  
  Purchase #7 $173.73   12.199%   $194.9233   $194.92   $194.90   $194.90  
  7 purchase totals = $776.36       $849.2659   $849.26   $849.25   $849.30