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 $64.44   10.731%   $71.3551   $71.36   $71.35   $71.40  
  Purchase #2 $228.80   4.688%   $239.5261   $239.53   $239.55   $239.50  
  Purchase #3 $98.43   7.205%   $105.5219   $105.52   $105.50   $105.50  
  Purchase #4 $237.72   12.390%   $267.1735   $267.17   $267.15   $267.20  
  Purchase #5 $58.46   13.308%   $66.2399   $66.24   $66.25   $66.20  
  Purchase #6 $97.28   5.713%   $102.8376   $102.84   $102.85   $102.80  
  Purchase #7 $18.43   9.113%   $20.1095   $20.11   $20.10   $20.10  
  7 purchase totals = $803.56       $872.7636   $872.77   $872.75   $872.70