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 $54.31   12.196%   $60.9336   $60.93   $60.95   $60.90  
  Purchase #2 $199.43   3.442%   $206.2944   $206.29   $206.30   $206.30  
  Purchase #3 $102.83   12.256%   $115.4328   $115.43   $115.45   $115.40  
  Purchase #4 $205.52   6.617%   $219.1193   $219.12   $219.10   $219.10  
  Purchase #5 $115.47   3.603%   $119.6304   $119.63   $119.65   $119.60  
  Purchase #6 $82.97   3.345%   $85.7453   $85.75   $85.75   $85.70  
  Purchase #7 $207.97   5.169%   $218.72   $218.72   $218.70   $218.70  
  7 purchase totals = $968.50       $1,025.8758   $1,025.87   $1,025.90   $1,025.70