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 $148.80   4.267%   $155.1493   $155.15   $155.15   $155.10  
  Purchase #2 $6.61   8.808%   $7.1922   $7.19   $7.20   $7.20  
  Purchase #3 $109.46   10.674%   $121.1438   $121.14   $121.15   $121.10  
  Purchase #4 $88.26   10.362%   $97.4055   $97.41   $97.40   $97.40  
  Purchase #5 $203.71   8.741%   $221.5163   $221.52   $221.50   $221.50  
  Purchase #6 $171.37   9.120%   $186.9989   $187.00   $187.00   $187.00  
  Purchase #7 $24.96   6.108%   $26.4846   $26.48   $26.50   $26.50  
  7 purchase totals = $753.17       $815.8906   $815.89   $815.90   $815.80