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 $242.29   5.420%   $255.4221   $255.42   $255.40   $255.40  
  Purchase #2 $24.64   8.526%   $26.7408   $26.74   $26.75   $26.70  
  Purchase #3 $246.27   3.357%   $254.5373   $254.54   $254.55   $254.50  
  Purchase #4 $230.90   6.764%   $246.5181   $246.52   $246.50   $246.50  
  Purchase #5 $159.96   5.572%   $168.873   $168.87   $168.85   $168.90  
  Purchase #6 $44.51   5.652%   $47.0257   $47.03   $47.05   $47.00  
  Purchase #7 $110.69   3.506%   $114.5708   $114.57   $114.55   $114.60  
  7 purchase totals = $1,059.26       $1,113.6878   $1,113.69   $1,113.65   $1,113.60