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 $60.88   5.683%   $64.3398   $64.34   $64.35   $64.30  
  Purchase #2 $246.77   7.200%   $264.5374   $264.54   $264.55   $264.50  
  Purchase #3 $148.69   6.696%   $158.6463   $158.65   $158.65   $158.60  
  Purchase #4 $26.38   11.251%   $29.348   $29.35   $29.35   $29.30  
  Purchase #5 $27.81   8.673%   $30.222   $30.22   $30.20   $30.20  
  Purchase #6 $219.61   5.415%   $231.5019   $231.50   $231.50   $231.50  
  Purchase #7 $87.52   13.522%   $99.3545   $99.35   $99.35   $99.40  
  7 purchase totals = $817.66       $877.9499   $877.95   $877.95   $877.80