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 $34.98   8.464%   $37.9407   $37.94   $37.95   $37.90  
  Purchase #2 $82.62   13.339%   $93.6407   $93.64   $93.65   $93.60  
  Purchase #3 $188.95   12.787%   $213.111   $213.11   $213.10   $213.10  
  Purchase #4 $122.65   10.446%   $135.462   $135.46   $135.45   $135.50  
  Purchase #5 $207.65   13.745%   $236.1915   $236.19   $236.20   $236.20  
  Purchase #6 $124.29   9.368%   $135.9335   $135.93   $135.95   $135.90  
  Purchase #7 $153.51   3.741%   $159.2528   $159.25   $159.25   $159.30  
  7 purchase totals = $914.65       $1,011.5322   $1,011.52   $1,011.55   $1,011.50