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 $219.61   11.537%   $244.9464   $244.95   $244.95   $244.90  
  Purchase #2 $67.57   5.771%   $71.4695   $71.47   $71.45   $71.50  
  Purchase #3 $79.98   4.584%   $83.6463   $83.65   $83.65   $83.60  
  Purchase #4 $180.73   11.465%   $201.4507   $201.45   $201.45   $201.50  
  Purchase #5 $168.31   7.462%   $180.8693   $180.87   $180.85   $180.90  
  Purchase #6 $18.47   11.797%   $20.6489   $20.65   $20.65   $20.60  
  Purchase #7 $250.33   6.811%   $267.38   $267.38   $267.40   $267.40  
  7 purchase totals = $985.00       $1,070.4111   $1,070.42   $1,070.40   $1,070.40