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 $82.59   6.753%   $88.1673   $88.17   $88.15   $88.20  
  Purchase #2 $161.52   11.622%   $180.2919   $180.29   $180.30   $180.30  
  Purchase #3 $209.34   10.699%   $231.7373   $231.74   $231.75   $231.70  
  Purchase #4 $233.64   3.688%   $242.2566   $242.26   $242.25   $242.30  
  Purchase #5 $82.75   13.681%   $94.071   $94.07   $94.05   $94.10  
  Purchase #6 $26.69   12.494%   $30.0246   $30.02   $30.00   $30.00  
  Purchase #7 $178.68   9.577%   $195.7922   $195.79   $195.80   $195.80  
  7 purchase totals = $975.21       $1,062.3409   $1,062.34   $1,062.30   $1,062.40