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 $106.38   11.835%   $118.9701   $118.97   $118.95   $119.00  
  Purchase #2 $63.56   7.336%   $68.2228   $68.22   $68.20   $68.20  
  Purchase #3 $93.87   6.210%   $99.6993   $99.70   $99.70   $99.70  
  Purchase #4 $158.31   10.171%   $174.4117   $174.41   $174.40   $174.40  
  Purchase #5 $250.62   5.457%   $264.2963   $264.30   $264.30   $264.30  
  Purchase #6 $109.45   8.755%   $119.0323   $119.03   $119.05   $119.00  
  Purchase #7 $6.38   13.808%   $7.261   $7.26   $7.25   $7.30  
  7 purchase totals = $788.57       $851.8935   $851.89   $851.85   $851.90