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 $184.33   13.118%   $208.5104   $208.51   $208.50   $208.50  
  Purchase #2 $232.58   7.305%   $249.57   $249.57   $249.55   $249.60  
  Purchase #3 $102.39   8.351%   $110.9406   $110.94   $110.95   $110.90  
  Purchase #4 $151.74   11.853%   $169.7257   $169.73   $169.75   $169.70  
  Purchase #5 $221.64   6.262%   $235.5191   $235.52   $235.50   $235.50  
  Purchase #6 $212.83   6.603%   $226.8832   $226.88   $226.90   $226.90  
  Purchase #7 $115.97   7.840%   $125.062   $125.06   $125.05   $125.10  
  7 purchase totals = $1,221.48       $1,326.2110   $1,326.21   $1,326.20   $1,326.20