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 $223.27   10.271%   $246.2021   $246.20   $246.20   $246.20  
  Purchase #2 $220.93   7.440%   $237.3672   $237.37   $237.35   $237.40  
  Purchase #3 $25.96   11.478%   $28.9397   $28.94   $28.95   $28.90  
  Purchase #4 $169.32   12.502%   $190.4884   $190.49   $190.50   $190.50  
  Purchase #5 $125.70   4.503%   $131.3603   $131.36   $131.35   $131.40  
  Purchase #6 $202.71   12.621%   $228.294   $228.29   $228.30   $228.30  
  Purchase #7 $224.49   7.690%   $241.7533   $241.75   $241.75   $241.80  
  7 purchase totals = $1,192.38       $1,304.4050   $1,304.40   $1,304.40   $1,304.50