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 $47.67   9.780%   $52.3321   $52.33   $52.35   $52.30  
  Purchase #2 $214.82   12.502%   $241.6768   $241.68   $241.70   $241.70  
  Purchase #3 $82.29   6.316%   $87.4874   $87.49   $87.50   $87.50  
  Purchase #4 $210.81   8.716%   $229.1842   $229.18   $229.20   $229.20  
  Purchase #5 $244.58   12.231%   $274.4946   $274.49   $274.50   $274.50  
  Purchase #6 $141.47   11.696%   $158.0163   $158.02   $158.00   $158.00  
  Purchase #7 $136.50   5.434%   $143.9174   $143.92   $143.90   $143.90  
  7 purchase totals = $1,078.14       $1,187.1088   $1,187.11   $1,187.15   $1,187.10