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 $91.69   8.288%   $99.2893   $99.29   $99.30   $99.30  
  Purchase #2 $87.52   7.393%   $93.9904   $93.99   $94.00   $94.00  
  Purchase #3 $55.95   5.415%   $58.9797   $58.98   $59.00   $59.00  
  Purchase #4 $176.92   10.421%   $195.3568   $195.36   $195.35   $195.40  
  Purchase #5 $185.44   4.199%   $193.2266   $193.23   $193.25   $193.20  
  Purchase #6 $249.72   10.344%   $275.551   $275.55   $275.55   $275.60  
  Purchase #7 $75.42   12.689%   $84.99   $84.99   $85.00   $85.00  
  7 purchase totals = $922.66       $1,001.3838   $1,001.39   $1,001.45   $1,001.50