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 $227.74   8.413%   $246.8998   $246.90   $246.90   $246.90  
  Purchase #2 $24.41   7.542%   $26.251   $26.25   $26.25   $26.30  
  Purchase #3 $160.33   6.600%   $170.9118   $170.91   $170.90   $170.90  
  Purchase #4 $174.45   13.533%   $198.0583   $198.06   $198.05   $198.10  
  Purchase #5 $183.30   4.491%   $191.532   $191.53   $191.55   $191.50  
  Purchase #6 $61.68   12.506%   $69.3937   $69.39   $69.40   $69.40  
  Purchase #7 $53.82   13.849%   $61.2735   $61.27   $61.25   $61.30  
  7 purchase totals = $885.73       $964.3201   $964.31   $964.30   $964.40