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 $41.29   11.742%   $46.1383   $46.14   $46.15   $46.10  
  Purchase #2 $218.84   3.497%   $226.4928   $226.49   $226.50   $226.50  
  Purchase #3 $93.49   9.845%   $102.6941   $102.69   $102.70   $102.70  
  Purchase #4 $224.64   13.404%   $254.7507   $254.75   $254.75   $254.80  
  Purchase #5 $236.40   12.147%   $265.1155   $265.12   $265.10   $265.10  
  Purchase #6 $69.96   9.387%   $76.5271   $76.53   $76.55   $76.50  
  Purchase #7 $69.57   11.410%   $77.5079   $77.51   $77.50   $77.50  
  7 purchase totals = $954.19       $1,049.2264   $1,049.23   $1,049.25   $1,049.20