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 $29.48   12.601%   $33.1948   $33.19   $33.20   $33.20  
  Purchase #2 $196.48   7.490%   $211.1964   $211.20   $211.20   $211.20  
  Purchase #3 $95.40   10.777%   $105.6813   $105.68   $105.70   $105.70  
  Purchase #4 $146.54   11.733%   $163.7335   $163.73   $163.75   $163.70  
  Purchase #5 $71.73   12.220%   $80.4954   $80.50   $80.50   $80.50  
  Purchase #6 $99.55   5.591%   $105.1158   $105.12   $105.10   $105.10  
  Purchase #7 $56.85   12.253%   $63.8158   $63.82   $63.80   $63.80  
  7 purchase totals = $696.03       $763.2330   $763.24   $763.25   $763.20