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 $69.57   13.474%   $78.9439   $78.94   $78.95   $78.90  
  Purchase #2 $5.83   9.696%   $6.3953   $6.40   $6.40   $6.40  
  Purchase #3 $134.61   12.712%   $151.7216   $151.72   $151.70   $151.70  
  Purchase #4 $54.42   7.766%   $58.6463   $58.65   $58.65   $58.60  
  Purchase #5 $202.42   6.142%   $214.8526   $214.85   $214.85   $214.90  
  Purchase #6 $72.27   6.417%   $76.9076   $76.91   $76.90   $76.90  
  Purchase #7 $210.69   3.476%   $218.0136   $218.01   $218.00   $218.00  
  7 purchase totals = $749.81       $805.4809   $805.48   $805.45   $805.40