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 $237.41   11.838%   $265.5146   $265.51   $265.50   $265.50  
  Purchase #2 $239.60   9.494%   $262.3476   $262.35   $262.35   $262.30  
  Purchase #3 $29.71   5.660%   $31.3916   $31.39   $31.40   $31.40  
  Purchase #4 $160.37   9.110%   $174.9797   $174.98   $175.00   $175.00  
  Purchase #5 $129.44   9.852%   $142.1924   $142.19   $142.20   $142.20  
  Purchase #6 $214.41   13.404%   $243.1495   $243.15   $243.15   $243.10  
  Purchase #7 $88.54   6.397%   $94.2039   $94.20   $94.20   $94.20  
  7 purchase totals = $1,099.48       $1,213.7793   $1,213.77   $1,213.80   $1,213.70