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 $72.64   6.253%   $77.1822   $77.18   $77.20   $77.20  
  Purchase #2 $247.33   9.651%   $271.1998   $271.20   $271.20   $271.20  
  Purchase #3 $20.68   8.668%   $22.4725   $22.47   $22.45   $22.50  
  Purchase #4 $79.89   7.225%   $85.6621   $85.66   $85.65   $85.70  
  Purchase #5 $220.40   11.577%   $245.9157   $245.92   $245.90   $245.90  
  Purchase #6 $196.62   11.726%   $219.6757   $219.68   $219.70   $219.70  
  Purchase #7 $229.28   6.290%   $243.7017   $243.70   $243.70   $243.70  
  7 purchase totals = $1,066.84       $1,165.8097   $1,165.81   $1,165.80   $1,165.90