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 $241.56   10.764%   $267.5615   $267.56   $267.55   $267.60  
  Purchase #2 $154.57   13.756%   $175.8326   $175.83   $175.85   $175.80  
  Purchase #3 $197.63   6.764%   $210.9977   $211.00   $211.00   $211.00  
  Purchase #4 $197.68   13.620%   $224.604   $224.60   $224.60   $224.60  
  Purchase #5 $44.29   10.426%   $48.9077   $48.91   $48.90   $48.90  
  Purchase #6 $8.26   12.806%   $9.3178   $9.32   $9.30   $9.30  
  Purchase #7 $57.35   5.442%   $60.471   $60.47   $60.45   $60.50  
  7 purchase totals = $901.34       $997.6923   $997.69   $997.65   $997.70