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 $70.84   6.651%   $75.5516   $75.55   $75.55   $75.60  
  Purchase #2 $218.39   9.760%   $239.7049   $239.70   $239.70   $239.70  
  Purchase #3 $246.79   3.412%   $255.2105   $255.21   $255.20   $255.20  
  Purchase #4 $144.59   6.710%   $154.292   $154.29   $154.30   $154.30  
  Purchase #5 $170.25   5.214%   $179.1268   $179.13   $179.15   $179.10  
  Purchase #6 $45.76   3.794%   $47.4961   $47.50   $47.50   $47.50  
  Purchase #7 $78.47   7.547%   $84.3921   $84.39   $84.40   $84.40  
  7 purchase totals = $975.09       $1,035.7740   $1,035.77   $1,035.80   $1,035.80