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 $206.49   12.579%   $232.4644   $232.46   $232.45   $232.50  
  Purchase #2 $100.77   13.421%   $114.2943   $114.29   $114.30   $114.30  
  Purchase #3 $82.72   13.187%   $93.6283   $93.63   $93.65   $93.60  
  Purchase #4 $247.86   11.651%   $276.7382   $276.74   $276.75   $276.70  
  Purchase #5 $102.72   13.178%   $116.2564   $116.26   $116.25   $116.30  
  Purchase #6 $243.62   7.625%   $262.196   $262.20   $262.20   $262.20  
  Purchase #7 $129.75   10.175%   $142.9521   $142.95   $142.95   $143.00  
  7 purchase totals = $1,113.93       $1,238.5297   $1,238.53   $1,238.55   $1,238.60