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 $47.94   11.579%   $53.491   $53.49   $53.50   $53.50  
  Purchase #2 $174.73   5.797%   $184.8591   $184.86   $184.85   $184.90  
  Purchase #3 $5.67   8.681%   $6.1622   $6.16   $6.15   $6.20  
  Purchase #4 $230.44   3.512%   $238.5331   $238.53   $238.55   $238.50  
  Purchase #5 $70.86   5.782%   $74.9571   $74.96   $74.95   $75.00  
  Purchase #6 $174.57   11.870%   $195.2915   $195.29   $195.30   $195.30  
  Purchase #7 $243.63   7.568%   $262.0679   $262.07   $262.05   $262.10  
  7 purchase totals = $947.84       $1,015.3619   $1,015.36   $1,015.35   $1,015.50