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 $154.69   12.822%   $174.5244   $174.52   $174.50   $174.50  
  Purchase #2 $187.95   8.236%   $203.4296   $203.43   $203.45   $203.40  
  Purchase #3 $43.66   6.339%   $46.4276   $46.43   $46.45   $46.40  
  Purchase #4 $237.31   7.833%   $255.8985   $255.90   $255.90   $255.90  
  Purchase #5 $122.66   3.524%   $126.9825   $126.98   $127.00   $127.00  
  Purchase #6 $93.57   10.851%   $103.7233   $103.72   $103.70   $103.70  
  Purchase #7 $11.55   10.547%   $12.7682   $12.77   $12.75   $12.80  
  7 purchase totals = $851.39       $923.7541   $923.75   $923.75   $923.70