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 $232.40   6.134%   $246.6554   $246.66   $246.65   $246.70  
  Purchase #2 $12.41   8.329%   $13.4436   $13.44   $13.45   $13.40  
  Purchase #3 $245.70   7.161%   $263.2946   $263.29   $263.30   $263.30  
  Purchase #4 $91.74   10.839%   $101.6837   $101.68   $101.70   $101.70  
  Purchase #5 $103.30   6.873%   $110.3998   $110.40   $110.40   $110.40  
  Purchase #6 $246.89   9.196%   $269.594   $269.59   $269.60   $269.60  
  Purchase #7 $43.30   3.597%   $44.8575   $44.86   $44.85   $44.90  
  7 purchase totals = $975.74       $1,049.9286   $1,049.92   $1,049.95   $1,050.00