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 $70.56   3.108%   $72.753   $72.75   $72.75   $72.80  
  Purchase #2 $127.55   6.204%   $135.4632   $135.46   $135.45   $135.50  
  Purchase #3 $123.79   3.517%   $128.1437   $128.14   $128.15   $128.10  
  Purchase #4 $154.99   6.123%   $164.48   $164.48   $164.50   $164.50  
  Purchase #5 $230.37   3.752%   $239.0135   $239.01   $239.00   $239.00  
  Purchase #6 $101.87   6.449%   $108.4396   $108.44   $108.45   $108.40  
  Purchase #7 $67.68   13.547%   $76.8486   $76.85   $76.85   $76.80  
  7 purchase totals = $876.81       $925.1416   $925.13   $925.15   $925.10