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 $215.50   12.145%   $241.6725   $241.67   $241.65   $241.70  
  Purchase #2 $194.77   8.268%   $210.8736   $210.87   $210.85   $210.90  
  Purchase #3 $228.66   12.424%   $257.0687   $257.07   $257.05   $257.10  
  Purchase #4 $48.62   12.742%   $54.8152   $54.82   $54.80   $54.80  
  Purchase #5 $174.52   11.357%   $194.3402   $194.34   $194.35   $194.30  
  Purchase #6 $214.91   3.512%   $222.4576   $222.46   $222.45   $222.50  
  Purchase #7 $163.37   11.680%   $182.4516   $182.45   $182.45   $182.50  
  7 purchase totals = $1,240.35       $1,363.6794   $1,363.68   $1,363.60   $1,363.80