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 $179.48   13.500%   $203.7098   $203.71   $203.70   $203.70  
  Purchase #2 $234.32   12.148%   $262.7852   $262.79   $262.80   $262.80  
  Purchase #3 $39.33   5.590%   $41.5285   $41.53   $41.55   $41.50  
  Purchase #4 $157.71   11.509%   $175.8608   $175.86   $175.85   $175.90  
  Purchase #5 $156.57   10.731%   $173.3715   $173.37   $173.35   $173.40  
  Purchase #6 $198.94   9.569%   $217.9766   $217.98   $218.00   $218.00  
  Purchase #7 $50.65   11.805%   $56.6292   $56.63   $56.65   $56.60  
  7 purchase totals = $1,017.00       $1,131.8616   $1,131.87   $1,131.90   $1,131.90