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 $236.52   13.374%   $268.1522   $268.15   $268.15   $268.20  
  Purchase #2 $169.42   13.526%   $192.3357   $192.34   $192.35   $192.30  
  Purchase #3 $41.60   11.699%   $46.4668   $46.47   $46.45   $46.50  
  Purchase #4 $198.71   13.417%   $225.3709   $225.37   $225.35   $225.40  
  Purchase #5 $225.54   7.144%   $241.6526   $241.65   $241.65   $241.70  
  Purchase #6 $83.99   13.638%   $95.4446   $95.44   $95.45   $95.40  
  Purchase #7 $41.53   8.327%   $44.9882   $44.99   $45.00   $45.00  
  7 purchase totals = $997.31       $1,114.4110   $1,114.41   $1,114.40   $1,114.50