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 $106.55   9.852%   $117.0473   $117.05   $117.05   $117.00  
  Purchase #2 $230.59   12.193%   $258.7058   $258.71   $258.70   $258.70  
  Purchase #3 $31.80   3.457%   $32.8993   $32.90   $32.90   $32.90  
  Purchase #4 $212.95   6.483%   $226.7555   $226.76   $226.75   $226.80  
  Purchase #5 $135.35   13.188%   $153.2   $153.20   $153.20   $153.20  
  Purchase #6 $231.92   3.691%   $240.4802   $240.48   $240.50   $240.50  
  Purchase #7 $217.84   7.394%   $233.9471   $233.95   $233.95   $233.90  
  7 purchase totals = $1,167.00       $1,263.0352   $1,263.05   $1,263.05   $1,263.00