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 $134.81   13.740%   $153.3329   $153.33   $153.35   $153.30  
  Purchase #2 $114.98   10.233%   $126.7459   $126.75   $126.75   $126.70  
  Purchase #3 $124.45   13.550%   $141.313   $141.31   $141.30   $141.30  
  Purchase #4 $162.90   11.794%   $182.1124   $182.11   $182.10   $182.10  
  Purchase #5 $71.54   8.232%   $77.4292   $77.43   $77.45   $77.40  
  Purchase #6 $246.38   8.722%   $267.8693   $267.87   $267.85   $267.90  
  Purchase #7 $20.39   6.827%   $21.782   $21.78   $21.80   $21.80  
  7 purchase totals = $875.45       $970.5847   $970.58   $970.60   $970.50