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 $232.43   9.206%   $253.8275   $253.83   $253.85   $253.80  
  Purchase #2 $131.81   11.315%   $146.7243   $146.72   $146.70   $146.70  
  Purchase #3 $53.66   13.457%   $60.881   $60.88   $60.90   $60.90  
  Purchase #4 $220.50   11.320%   $245.4606   $245.46   $245.45   $245.50  
  Purchase #5 $217.75   5.842%   $230.471   $230.47   $230.45   $230.50  
  Purchase #6 $220.89   3.627%   $228.9017   $228.90   $228.90   $228.90  
  Purchase #7 $241.40   4.737%   $252.8351   $252.84   $252.85   $252.80  
  7 purchase totals = $1,318.44       $1,419.1012   $1,419.10   $1,419.10   $1,419.10