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 $170.41   13.516%   $193.4426   $193.44   $193.45   $193.40  
  Purchase #2 $236.69   13.333%   $268.2479   $268.25   $268.25   $268.20  
  Purchase #3 $108.39   4.367%   $113.1234   $113.12   $113.10   $113.10  
  Purchase #4 $189.30   6.714%   $202.0096   $202.01   $202.00   $202.00  
  Purchase #5 $83.34   11.273%   $92.7349   $92.73   $92.75   $92.70  
  Purchase #6 $160.50   6.855%   $171.5023   $171.50   $171.50   $171.50  
  Purchase #7 $113.64   6.583%   $121.1209   $121.12   $121.10   $121.10  
  7 purchase totals = $1,062.27       $1,162.1816   $1,162.17   $1,162.15   $1,162.00