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 $142.85   13.164%   $161.6548   $161.65   $161.65   $161.70  
  Purchase #2 $226.60   4.435%   $236.6497   $236.65   $236.65   $236.60  
  Purchase #3 $134.57   11.227%   $149.6782   $149.68   $149.70   $149.70  
  Purchase #4 $107.53   11.381%   $119.768   $119.77   $119.75   $119.80  
  Purchase #5 $66.99   11.347%   $74.5914   $74.59   $74.60   $74.60  
  Purchase #6 $167.93   11.250%   $186.8221   $186.82   $186.80   $186.80  
  Purchase #7 $100.33   6.796%   $107.1484   $107.15   $107.15   $107.10  
  7 purchase totals = $946.80       $1,036.3126   $1,036.31   $1,036.30   $1,036.30