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 $239.64   10.418%   $264.6057   $264.61   $264.60   $264.60  
  Purchase #2 $96.96   13.814%   $110.3541   $110.35   $110.35   $110.40  
  Purchase #3 $65.26   11.475%   $72.7486   $72.75   $72.75   $72.70  
  Purchase #4 $164.29   7.622%   $176.8122   $176.81   $176.80   $176.80  
  Purchase #5 $65.63   9.381%   $71.7868   $71.79   $71.80   $71.80  
  Purchase #6 $187.78   7.682%   $202.2053   $202.21   $202.20   $202.20  
  Purchase #7 $142.86   7.659%   $153.8016   $153.80   $153.80   $153.80  
  7 purchase totals = $962.42       $1,052.3143   $1,052.32   $1,052.30   $1,052.30