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 $69.98   6.455%   $74.4972   $74.50   $74.50   $74.50  
  Purchase #2 $111.84   10.163%   $123.2063   $123.21   $123.20   $123.20  
  Purchase #3 $70.50   6.372%   $74.9923   $74.99   $75.00   $75.00  
  Purchase #4 $136.56   12.649%   $153.8335   $153.83   $153.85   $153.80  
  Purchase #5 $241.62   6.717%   $257.8496   $257.85   $257.85   $257.80  
  Purchase #6 $141.32   10.636%   $156.3508   $156.35   $156.35   $156.40  
  Purchase #7 $215.71   6.226%   $229.1401   $229.14   $229.15   $229.10  
  7 purchase totals = $987.53       $1,069.8698   $1,069.87   $1,069.90   $1,069.80