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 $245.72   8.582%   $266.8077   $266.81   $266.80   $266.80  
  Purchase #2 $26.37   13.647%   $29.9687   $29.97   $29.95   $30.00  
  Purchase #3 $119.42   4.144%   $124.3688   $124.37   $124.35   $124.40  
  Purchase #4 $207.70   9.379%   $227.1802   $227.18   $227.20   $227.20  
  Purchase #5 $233.85   5.637%   $247.0321   $247.03   $247.05   $247.00  
  Purchase #6 $86.82   4.869%   $91.0473   $91.05   $91.05   $91.00  
  Purchase #7 $46.56   4.159%   $48.4964   $48.50   $48.50   $48.50  
  7 purchase totals = $966.44       $1,034.9012   $1,034.91   $1,034.90   $1,034.90