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 $232.83   11.482%   $259.5635   $259.56   $259.55   $259.60  
  Purchase #2 $22.48   9.288%   $24.5679   $24.57   $24.55   $24.60  
  Purchase #3 $178.46   12.346%   $200.4927   $200.49   $200.50   $200.50  
  Purchase #4 $74.93   6.178%   $79.5592   $79.56   $79.55   $79.60  
  Purchase #5 $235.64   3.686%   $244.3257   $244.33   $244.35   $244.30  
  Purchase #6 $66.41   7.178%   $71.1769   $71.18   $71.20   $71.20  
  Purchase #7 $126.39   5.359%   $133.1632   $133.16   $133.15   $133.20  
  7 purchase totals = $937.14       $1,012.8491   $1,012.85   $1,012.85   $1,013.00