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 $183.48   11.413%   $204.4206   $204.42   $204.40   $204.40  
  Purchase #2 $42.52   3.817%   $44.143   $44.14   $44.15   $44.10  
  Purchase #3 $23.61   11.536%   $26.3336   $26.33   $26.35   $26.30  
  Purchase #4 $6.77   11.417%   $7.5429   $7.54   $7.55   $7.50  
  Purchase #5 $163.80   6.614%   $174.6337   $174.63   $174.65   $174.60  
  Purchase #6 $72.56   3.312%   $74.9632   $74.96   $74.95   $75.00  
  Purchase #7 $75.34   4.453%   $78.6949   $78.69   $78.70   $78.70  
  7 purchase totals = $568.08       $610.7319   $610.71   $610.75   $610.60