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 $224.54   7.766%   $241.9778   $241.98   $242.00   $242.00  
  Purchase #2 $209.51   4.815%   $219.5979   $219.60   $219.60   $219.60  
  Purchase #3 $195.47   11.737%   $218.4123   $218.41   $218.40   $218.40  
  Purchase #4 $49.26   5.191%   $51.8171   $51.82   $51.80   $51.80  
  Purchase #5 $25.32   4.212%   $26.3865   $26.39   $26.40   $26.40  
  Purchase #6 $40.78   13.603%   $46.3273   $46.33   $46.35   $46.30  
  Purchase #7 $179.37   13.785%   $204.0962   $204.10   $204.10   $204.10  
  7 purchase totals = $924.25       $1,008.6151   $1,008.63   $1,008.65   $1,008.60