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 $47.56   11.372%   $52.9685   $52.97   $52.95   $53.00  
  Purchase #2 $137.44   10.597%   $152.0045   $152.00   $152.00   $152.00  
  Purchase #3 $208.25   12.165%   $233.5836   $233.58   $233.60   $233.60  
  Purchase #4 $227.94   8.138%   $246.4898   $246.49   $246.50   $246.50  
  Purchase #5 $204.30   7.340%   $219.2956   $219.30   $219.30   $219.30  
  Purchase #6 $242.70   9.582%   $265.9555   $265.96   $265.95   $266.00  
  Purchase #7 $164.86   11.870%   $184.4289   $184.43   $184.45   $184.40  
  7 purchase totals = $1,233.05       $1,354.7264   $1,354.73   $1,354.75   $1,354.80