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 $235.54   10.473%   $260.2081   $260.21   $260.20   $260.20  
  Purchase #2 $201.52   6.241%   $214.0969   $214.10   $214.10   $214.10  
  Purchase #3 $112.28   6.694%   $119.796   $119.80   $119.80   $119.80  
  Purchase #4 $26.92   13.343%   $30.5119   $30.51   $30.50   $30.50  
  Purchase #5 $198.92   8.709%   $216.2439   $216.24   $216.25   $216.20  
  Purchase #6 $31.75   12.211%   $35.627   $35.63   $35.65   $35.60  
  Purchase #7 $156.55   8.388%   $169.6814   $169.68   $169.70   $169.70  
  7 purchase totals = $963.48       $1,046.1652   $1,046.17   $1,046.20   $1,046.10