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 $136.74   12.391%   $153.6835   $153.68   $153.70   $153.70  
  Purchase #2 $230.64   6.791%   $246.3028   $246.30   $246.30   $246.30  
  Purchase #3 $248.76   5.205%   $261.708   $261.71   $261.70   $261.70  
  Purchase #4 $206.45   10.793%   $228.7321   $228.73   $228.75   $228.70  
  Purchase #5 $44.89   9.416%   $49.1168   $49.12   $49.10   $49.10  
  Purchase #6 $68.45   6.179%   $72.6795   $72.68   $72.70   $72.70  
  Purchase #7 $230.43   5.272%   $242.5783   $242.58   $242.60   $242.60  
  7 purchase totals = $1,166.36       $1,254.8010   $1,254.80   $1,254.85   $1,254.80