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 $64.81   8.802%   $70.5146   $70.51   $70.50   $70.50  
  Purchase #2 $52.62   7.760%   $56.7033   $56.70   $56.70   $56.70  
  Purchase #3 $44.34   6.148%   $47.066   $47.07   $47.05   $47.10  
  Purchase #4 $159.69   7.119%   $171.0583   $171.06   $171.05   $171.10  
  Purchase #5 $105.29   11.770%   $117.6826   $117.68   $117.70   $117.70  
  Purchase #6 $117.98   10.840%   $130.769   $130.77   $130.75   $130.80  
  Purchase #7 $148.73   4.764%   $155.8155   $155.82   $155.80   $155.80  
  7 purchase totals = $693.46       $749.6093   $749.61   $749.55   $749.70