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 $60.94   11.170%   $67.747   $67.75   $67.75   $67.70  
  Purchase #2 $165.56   7.529%   $178.025   $178.03   $178.05   $178.00  
  Purchase #3 $152.32   3.435%   $157.5522   $157.55   $157.55   $157.60  
  Purchase #4 $104.65   13.260%   $118.5266   $118.53   $118.55   $118.50  
  Purchase #5 $102.86   12.339%   $115.5519   $115.55   $115.55   $115.60  
  Purchase #6 $126.85   5.543%   $133.8813   $133.88   $133.90   $133.90  
  Purchase #7 $29.36   13.663%   $33.3715   $33.37   $33.35   $33.40  
  7 purchase totals = $742.54       $804.6555   $804.66   $804.70   $804.70