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 $95.81   7.650%   $103.1395   $103.14   $103.15   $103.10  
  Purchase #2 $11.96   13.224%   $13.5416   $13.54   $13.55   $13.50  
  Purchase #3 $39.62   5.463%   $41.7844   $41.78   $41.80   $41.80  
  Purchase #4 $168.99   8.581%   $183.491   $183.49   $183.50   $183.50  
  Purchase #5 $62.38   4.721%   $65.325   $65.33   $65.35   $65.30  
  Purchase #6 $244.71   4.154%   $254.8753   $254.88   $254.90   $254.90  
  Purchase #7 $183.82   8.274%   $199.0293   $199.03   $199.05   $199.00  
  7 purchase totals = $807.29       $861.1861   $861.19   $861.30   $861.10