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 $209.74   12.621%   $236.2113   $236.21   $236.20   $236.20  
  Purchase #2 $192.71   6.858%   $205.9261   $205.93   $205.95   $205.90  
  Purchase #3 $64.37   12.575%   $72.4645   $72.46   $72.45   $72.50  
  Purchase #4 $181.87   9.717%   $199.5423   $199.54   $199.55   $199.50  
  Purchase #5 $46.44   4.238%   $48.4081   $48.41   $48.40   $48.40  
  Purchase #6 $204.94   9.855%   $225.1368   $225.14   $225.15   $225.10  
  Purchase #7 $65.95   11.696%   $73.6635   $73.66   $73.65   $73.70  
  7 purchase totals = $966.02       $1,061.3526   $1,061.35   $1,061.35   $1,061.30