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 $58.88   5.809%   $62.3003   $62.30   $62.30   $62.30  
  Purchase #2 $170.73   4.252%   $177.9894   $177.99   $178.00   $178.00  
  Purchase #3 $87.75   4.717%   $91.8892   $91.89   $91.90   $91.90  
  Purchase #4 $13.74   11.632%   $15.3382   $15.34   $15.35   $15.30  
  Purchase #5 $121.61   3.777%   $126.2032   $126.20   $126.20   $126.20  
  Purchase #6 $7.71   11.617%   $8.6057   $8.61   $8.60   $8.60  
  Purchase #7 $81.47   4.255%   $84.9365   $84.94   $84.95   $84.90  
  7 purchase totals = $541.89       $567.2625   $567.27   $567.30   $567.20