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 $66.49   10.106%   $73.2095   $73.21   $73.20   $73.20  
  Purchase #2 $222.93   9.471%   $244.0437   $244.04   $244.05   $244.00  
  Purchase #3 $249.51   12.348%   $280.3195   $280.32   $280.30   $280.30  
  Purchase #4 $44.84   6.846%   $47.9097   $47.91   $47.90   $47.90  
  Purchase #5 $68.58   7.760%   $73.9018   $73.90   $73.90   $73.90  
  Purchase #6 $239.72   5.753%   $253.5111   $253.51   $253.50   $253.50  
  Purchase #7 $171.96   7.411%   $184.704   $184.70   $184.70   $184.70  
  7 purchase totals = $1,064.03       $1,157.5993   $1,157.59   $1,157.55   $1,157.50