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 $205.72   13.362%   $233.2083   $233.21   $233.20   $233.20  
  Purchase #2 $38.52   7.532%   $41.4213   $41.42   $41.40   $41.40  
  Purchase #3 $224.36   11.208%   $249.5063   $249.51   $249.50   $249.50  
  Purchase #4 $95.73   11.732%   $106.961   $106.96   $106.95   $107.00  
  Purchase #5 $196.70   3.239%   $203.0711   $203.07   $203.05   $203.10  
  Purchase #6 $220.66   10.186%   $243.1364   $243.14   $243.15   $243.10  
  Purchase #7 $108.80   5.494%   $114.7775   $114.78   $114.80   $114.80  
  7 purchase totals = $1,090.49       $1,192.0819   $1,192.09   $1,192.05   $1,192.10