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 $24.73   8.764%   $26.8973   $26.90   $26.90   $26.90  
  Purchase #2 $133.57   12.230%   $149.9056   $149.91   $149.90   $149.90  
  Purchase #3 $219.96   11.757%   $245.8207   $245.82   $245.80   $245.80  
  Purchase #4 $55.43   7.655%   $59.6732   $59.67   $59.65   $59.70  
  Purchase #5 $204.70   12.813%   $230.9282   $230.93   $230.95   $230.90  
  Purchase #6 $228.41   6.379%   $242.9803   $242.98   $243.00   $243.00  
  Purchase #7 $78.36   10.519%   $86.6027   $86.60   $86.60   $86.60  
  7 purchase totals = $945.16       $1,042.8080   $1,042.81   $1,042.80   $1,042.80