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 $24.44   6.238%   $25.9646   $25.96   $25.95   $26.00  
  Purchase #2 $191.68   4.457%   $200.2232   $200.22   $200.20   $200.20  
  Purchase #3 $62.94   13.656%   $71.5351   $71.54   $71.55   $71.50  
  Purchase #4 $159.85   11.852%   $178.7954   $178.80   $178.80   $178.80  
  Purchase #5 $97.37   5.252%   $102.4839   $102.48   $102.50   $102.50  
  Purchase #6 $148.52   3.708%   $154.0271   $154.03   $154.05   $154.00  
  Purchase #7 $36.70   4.422%   $38.3229   $38.32   $38.30   $38.30  
  7 purchase totals = $721.50       $771.3522   $771.35   $771.35   $771.30