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 $222.74   9.471%   $243.8357   $243.84   $243.85   $243.80  
  Purchase #2 $206.77   10.572%   $228.6297   $228.63   $228.65   $228.60  
  Purchase #3 $87.84   11.190%   $97.6693   $97.67   $97.65   $97.70  
  Purchase #4 $157.98   13.682%   $179.5948   $179.59   $179.60   $179.60  
  Purchase #5 $121.62   3.124%   $125.4194   $125.42   $125.40   $125.40  
  Purchase #6 $57.80   3.664%   $59.9178   $59.92   $59.90   $59.90  
  Purchase #7 $107.64   6.302%   $114.4235   $114.42   $114.40   $114.40  
  7 purchase totals = $962.39       $1,049.4902   $1,049.49   $1,049.45   $1,049.40