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 $236.91   7.640%   $255.0099   $255.01   $255.00   $255.00  
  Purchase #2 $118.66   9.726%   $130.2009   $130.20   $130.20   $130.20  
  Purchase #3 $195.40   11.490%   $217.8515   $217.85   $217.85   $217.90  
  Purchase #4 $35.86   6.182%   $38.0769   $38.08   $38.10   $38.10  
  Purchase #5 $170.68   7.286%   $183.1157   $183.12   $183.10   $183.10  
  Purchase #6 $229.80   3.210%   $237.1766   $237.18   $237.20   $237.20  
  Purchase #7 $58.56   11.460%   $65.271   $65.27   $65.25   $65.30  
  7 purchase totals = $1,045.87       $1,126.7025   $1,126.71   $1,126.70   $1,126.80