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 $241.29   6.818%   $257.7412   $257.74   $257.75   $257.70  
  Purchase #2 $66.52   7.702%   $71.6434   $71.64   $71.65   $71.60  
  Purchase #3 $23.96   12.486%   $26.9516   $26.95   $26.95   $27.00  
  Purchase #4 $90.97   4.790%   $95.3275   $95.33   $95.35   $95.30  
  Purchase #5 $232.50   9.163%   $253.804   $253.80   $253.80   $253.80  
  Purchase #6 $149.56   13.198%   $169.2989   $169.30   $169.30   $169.30  
  Purchase #7 $89.97   3.389%   $93.0191   $93.02   $93.00   $93.00  
  7 purchase totals = $894.77       $967.7857   $967.78   $967.80   $967.70