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 $61.47   12.741%   $69.3019   $69.30   $69.30   $69.30  
  Purchase #2 $160.65   11.392%   $178.9512   $178.95   $178.95   $179.00  
  Purchase #3 $21.69   6.284%   $23.053   $23.05   $23.05   $23.10  
  Purchase #4 $227.78   9.771%   $250.0364   $250.04   $250.05   $250.00  
  Purchase #5 $123.40   4.360%   $128.7802   $128.78   $128.80   $128.80  
  Purchase #6 $194.38   9.783%   $213.3962   $213.40   $213.40   $213.40  
  Purchase #7 $13.51   5.592%   $14.2655   $14.27   $14.25   $14.30  
  7 purchase totals = $802.88       $877.7844   $877.79   $877.80   $877.90