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 $202.85   11.869%   $226.9263   $226.93   $226.95   $226.90  
  Purchase #2 $70.31   8.558%   $76.3271   $76.33   $76.35   $76.30  
  Purchase #3 $23.98   10.399%   $26.4737   $26.47   $26.45   $26.50  
  Purchase #4 $41.61   3.781%   $43.1833   $43.18   $43.20   $43.20  
  Purchase #5 $101.70   13.632%   $115.5637   $115.56   $115.55   $115.60  
  Purchase #6 $210.87   10.206%   $232.3914   $232.39   $232.40   $232.40  
  Purchase #7 $23.91   9.658%   $26.2192   $26.22   $26.20   $26.20  
  7 purchase totals = $675.23       $747.0847   $747.08   $747.10   $747.10