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 $139.49   11.594%   $155.6625   $155.66   $155.65   $155.70  
  Purchase #2 $174.86   8.251%   $189.2877   $189.29   $189.30   $189.30  
  Purchase #3 $95.73   11.587%   $106.8222   $106.82   $106.80   $106.80  
  Purchase #4 $97.83   4.787%   $102.5131   $102.51   $102.50   $102.50  
  Purchase #5 $169.89   7.679%   $182.9359   $182.94   $182.95   $182.90  
  Purchase #6 $119.52   6.757%   $127.596   $127.60   $127.60   $127.60  
  Purchase #7 $242.71   7.129%   $260.0128   $260.01   $260.00   $260.00  
  7 purchase totals = $1,040.03       $1,124.8302   $1,124.83   $1,124.80   $1,124.80