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 $52.34   13.273%   $59.2871   $59.29   $59.30   $59.30  
  Purchase #2 $168.46   11.480%   $187.7992   $187.80   $187.80   $187.80  
  Purchase #3 $242.84   8.128%   $262.578   $262.58   $262.60   $262.60  
  Purchase #4 $243.94   13.845%   $277.7135   $277.71   $277.70   $277.70  
  Purchase #5 $123.39   8.345%   $133.6869   $133.69   $133.70   $133.70  
  Purchase #6 $250.98   13.282%   $284.3152   $284.32   $284.30   $284.30  
  Purchase #7 $214.85   6.507%   $228.8303   $228.83   $228.85   $228.80  
  7 purchase totals = $1,296.80       $1,434.2102   $1,434.22   $1,434.25   $1,434.20