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 $103.51   10.284%   $114.155   $114.16   $114.15   $114.20  
  Purchase #2 $164.59   3.216%   $169.8832   $169.88   $169.90   $169.90  
  Purchase #3 $52.57   12.222%   $58.9951   $59.00   $59.00   $59.00  
  Purchase #4 $233.49   13.113%   $264.1075   $264.11   $264.10   $264.10  
  Purchase #5 $35.39   13.218%   $40.0679   $40.07   $40.05   $40.10  
  Purchase #6 $99.56   9.207%   $108.7265   $108.73   $108.75   $108.70  
  Purchase #7 $209.65   10.849%   $232.3949   $232.39   $232.40   $232.40  
  7 purchase totals = $898.76       $988.3301   $988.34   $988.35   $988.40