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 $226.77   6.280%   $241.0112   $241.01   $241.00   $241.00  
  Purchase #2 $180.50   7.170%   $193.4419   $193.44   $193.45   $193.40  
  Purchase #3 $67.50   12.578%   $75.9902   $75.99   $76.00   $76.00  
  Purchase #4 $102.80   13.871%   $117.0594   $117.06   $117.05   $117.10  
  Purchase #5 $31.69   13.645%   $36.0141   $36.01   $36.00   $36.00  
  Purchase #6 $208.37   10.460%   $230.1655   $230.17   $230.15   $230.20  
  Purchase #7 $116.99   3.441%   $121.0156   $121.02   $121.00   $121.00  
  7 purchase totals = $934.62       $1,014.6979   $1,014.70   $1,014.65   $1,014.70