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 $224.73   7.138%   $240.7712   $240.77   $240.75   $240.80  
  Purchase #2 $104.82   9.394%   $114.6668   $114.67   $114.65   $114.70  
  Purchase #3 $147.72   8.199%   $159.8316   $159.83   $159.85   $159.80  
  Purchase #4 $199.43   11.408%   $222.181   $222.18   $222.20   $222.20  
  Purchase #5 $201.36   6.457%   $214.3618   $214.36   $214.35   $214.40  
  Purchase #6 $186.92   8.464%   $202.7409   $202.74   $202.75   $202.70  
  Purchase #7 $196.82   5.314%   $207.279   $207.28   $207.30   $207.30  
  7 purchase totals = $1,261.80       $1,361.8323   $1,361.83   $1,361.85   $1,361.90