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 $246.65   12.202%   $276.7462   $276.75   $276.75   $276.70  
  Purchase #2 $41.67   7.457%   $44.7773   $44.78   $44.80   $44.80  
  Purchase #3 $161.49   13.119%   $182.6759   $182.68   $182.70   $182.70  
  Purchase #4 $40.92   9.561%   $44.8324   $44.83   $44.85   $44.80  
  Purchase #5 $85.30   11.389%   $95.0148   $95.01   $95.00   $95.00  
  Purchase #6 $189.44   8.591%   $205.7148   $205.71   $205.70   $205.70  
  Purchase #7 $190.44   5.347%   $200.6228   $200.62   $200.60   $200.60  
  7 purchase totals = $955.91       $1,050.3842   $1,050.38   $1,050.40   $1,050.30