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 $206.41   5.285%   $217.3188   $217.32   $217.30   $217.30  
  Purchase #2 $126.83   12.710%   $142.9501   $142.95   $142.95   $143.00  
  Purchase #3 $178.52   11.266%   $198.6321   $198.63   $198.65   $198.60  
  Purchase #4 $244.45   4.835%   $256.2692   $256.27   $256.25   $256.30  
  Purchase #5 $53.56   12.310%   $60.1532   $60.15   $60.15   $60.20  
  Purchase #6 $193.85   13.232%   $219.5002   $219.50   $219.50   $219.50  
  Purchase #7 $157.31   11.512%   $175.4195   $175.42   $175.40   $175.40  
  7 purchase totals = $1,160.93       $1,270.2431   $1,270.24   $1,270.20   $1,270.30