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 $87.76   12.129%   $98.4044   $98.40   $98.40   $98.40  
  Purchase #2 $110.44   6.353%   $117.4563   $117.46   $117.45   $117.50  
  Purchase #3 $160.41   8.477%   $174.008   $174.01   $174.00   $174.00  
  Purchase #4 $59.37   10.272%   $65.4685   $65.47   $65.45   $65.50  
  Purchase #5 $205.38   9.667%   $225.2341   $225.23   $225.25   $225.20  
  Purchase #6 $212.29   3.800%   $220.357   $220.36   $220.35   $220.40  
  Purchase #7 $114.82   10.312%   $126.6602   $126.66   $126.65   $126.70  
  7 purchase totals = $950.47       $1,027.5885   $1,027.59   $1,027.55   $1,027.70