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 $128.82   11.758%   $143.9667   $143.97   $143.95   $144.00  
  Purchase #2 $96.39   3.171%   $99.4465   $99.45   $99.45   $99.40  
  Purchase #3 $94.91   3.601%   $98.3277   $98.33   $98.35   $98.30  
  Purchase #4 $191.42   3.698%   $198.4987   $198.50   $198.50   $198.50  
  Purchase #5 $170.25   4.297%   $177.5656   $177.57   $177.55   $177.60  
  Purchase #6 $94.67   3.372%   $97.8623   $97.86   $97.85   $97.90  
  Purchase #7 $75.32   5.489%   $79.4543   $79.45   $79.45   $79.50  
  7 purchase totals = $851.78       $895.1218   $895.13   $895.10   $895.20