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   10.230%   $247.5104   $247.51   $247.50   $247.50  
  Purchase #2 $119.67   6.805%   $127.8135   $127.81   $127.80   $127.80  
  Purchase #3 $157.80   11.474%   $175.906   $175.91   $175.90   $175.90  
  Purchase #4 $49.26   13.573%   $55.9461   $55.95   $55.95   $55.90  
  Purchase #5 $196.83   3.750%   $204.2111   $204.21   $204.20   $204.20  
  Purchase #6 $67.73   11.234%   $75.3388   $75.34   $75.35   $75.30  
  Purchase #7 $250.57   8.551%   $271.9962   $272.00   $272.00   $272.00  
  7 purchase totals = $1,066.40       $1,158.7221   $1,158.73   $1,158.70   $1,158.60