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 $36.73   12.823%   $41.4399   $41.44   $41.45   $41.40  
  Purchase #2 $88.57   13.587%   $100.604   $100.60   $100.60   $100.60  
  Purchase #3 $12.41   8.793%   $13.5012   $13.50   $13.50   $13.50  
  Purchase #4 $249.85   5.282%   $263.0471   $263.05   $263.05   $263.00  
  Purchase #5 $215.45   4.304%   $224.723   $224.72   $224.70   $224.70  
  Purchase #6 $162.93   11.746%   $182.0678   $182.07   $182.05   $182.10  
  Purchase #7 $169.83   8.734%   $184.663   $184.66   $184.65   $184.70  
  7 purchase totals = $935.77       $1,010.0460   $1,010.04   $1,010.00   $1,010.00