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 $247.86   6.318%   $263.5198   $263.52   $263.50   $263.50  
  Purchase #2 $67.38   10.199%   $74.2521   $74.25   $74.25   $74.30  
  Purchase #3 $154.43   6.449%   $164.3892   $164.39   $164.40   $164.40  
  Purchase #4 $12.77   13.530%   $14.4978   $14.50   $14.50   $14.50  
  Purchase #5 $145.65   11.655%   $162.6255   $162.63   $162.65   $162.60  
  Purchase #6 $101.39   8.672%   $110.1825   $110.18   $110.20   $110.20  
  Purchase #7 $25.37   6.247%   $26.9549   $26.95   $26.95   $27.00  
  7 purchase totals = $754.85       $816.4218   $816.42   $816.45   $816.50