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 $248.25   11.677%   $277.2382   $277.24   $277.25   $277.20  
  Purchase #2 $111.94   4.332%   $116.7892   $116.79   $116.80   $116.80  
  Purchase #3 $76.41   4.146%   $79.578   $79.58   $79.60   $79.60  
  Purchase #4 $89.93   9.195%   $98.1991   $98.20   $98.20   $98.20  
  Purchase #5 $204.46   10.201%   $225.317   $225.32   $225.30   $225.30  
  Purchase #6 $142.55   10.662%   $157.7487   $157.75   $157.75   $157.70  
  Purchase #7 $22.31   13.535%   $25.3297   $25.33   $25.35   $25.30  
  7 purchase totals = $895.85       $980.1999   $980.21   $980.25   $980.10