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 $52.69   11.866%   $58.9422   $58.94   $58.95   $58.90  
  Purchase #2 $167.79   9.453%   $183.6512   $183.65   $183.65   $183.70  
  Purchase #3 $195.56   10.745%   $216.5729   $216.57   $216.55   $216.60  
  Purchase #4 $133.36   8.572%   $144.7916   $144.79   $144.80   $144.80  
  Purchase #5 $162.68   5.561%   $171.7266   $171.73   $171.75   $171.70  
  Purchase #6 $211.75   9.426%   $231.7096   $231.71   $231.70   $231.70  
  Purchase #7 $202.77   11.343%   $225.7702   $225.77   $225.75   $225.80  
  7 purchase totals = $1,126.60       $1,233.1643   $1,233.16   $1,233.15   $1,233.20