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 $49.46   12.684%   $55.7335   $55.73   $55.75   $55.70  
  Purchase #2 $176.71   3.107%   $182.2004   $182.20   $182.20   $182.20  
  Purchase #3 $20.84   9.480%   $22.8156   $22.82   $22.80   $22.80  
  Purchase #4 $74.52   6.400%   $79.2893   $79.29   $79.30   $79.30  
  Purchase #5 $99.26   4.641%   $103.8667   $103.87   $103.85   $103.90  
  Purchase #6 $195.49   4.871%   $205.0123   $205.01   $205.00   $205.00  
  Purchase #7 $89.81   8.254%   $97.2229   $97.22   $97.20   $97.20  
  7 purchase totals = $706.09       $746.1407   $746.14   $746.10   $746.10