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 $184.54   11.810%   $206.3342   $206.33   $206.35   $206.30  
  Purchase #2 $202.93   13.567%   $230.4615   $230.46   $230.45   $230.50  
  Purchase #3 $242.85   9.457%   $265.8163   $265.82   $265.80   $265.80  
  Purchase #4 $88.78   3.518%   $91.9033   $91.90   $91.90   $91.90  
  Purchase #5 $131.86   8.365%   $142.8901   $142.89   $142.90   $142.90  
  Purchase #6 $170.77   10.678%   $189.0048   $189.00   $189.00   $189.00  
  Purchase #7 $180.92   10.322%   $199.5946   $199.59   $199.60   $199.60  
  7 purchase totals = $1,202.65       $1,326.0048   $1,325.99   $1,326.00   $1,326.00