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 $34.82   9.535%   $38.1401   $38.14   $38.15   $38.10  
  Purchase #2 $101.88   8.232%   $110.2668   $110.27   $110.25   $110.30  
  Purchase #3 $83.46   11.439%   $93.007   $93.01   $93.00   $93.00  
  Purchase #4 $86.76   9.569%   $95.0621   $95.06   $95.05   $95.10  
  Purchase #5 $68.96   6.280%   $73.2907   $73.29   $73.30   $73.30  
  Purchase #6 $166.89   6.286%   $177.3807   $177.38   $177.40   $177.40  
  Purchase #7 $213.47   11.289%   $237.5686   $237.57   $237.55   $237.60  
  7 purchase totals = $756.24       $824.7160   $824.72   $824.70   $824.80