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 $74.74   11.756%   $83.5264   $83.53   $83.55   $83.50  
  Purchase #2 $211.28   13.397%   $239.5852   $239.59   $239.60   $239.60  
  Purchase #3 $56.34   9.430%   $61.6529   $61.65   $61.65   $61.70  
  Purchase #4 $218.84   3.605%   $226.7292   $226.73   $226.75   $226.70  
  Purchase #5 $56.96   5.318%   $59.9891   $59.99   $60.00   $60.00  
  Purchase #6 $67.74   8.778%   $73.6862   $73.69   $73.70   $73.70  
  Purchase #7 $178.85   9.758%   $196.3022   $196.30   $196.30   $196.30  
  7 purchase totals = $864.75       $941.4712   $941.48   $941.55   $941.50