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 $201.30   11.276%   $223.9986   $224.00   $224.00   $224.00  
  Purchase #2 $65.33   12.123%   $73.25   $73.25   $73.25   $73.30  
  Purchase #3 $168.82   13.513%   $191.6326   $191.63   $191.65   $191.60  
  Purchase #4 $243.60   12.674%   $274.4739   $274.47   $274.45   $274.50  
  Purchase #5 $187.44   3.418%   $193.8467   $193.85   $193.85   $193.80  
  Purchase #6 $146.71   13.464%   $166.463   $166.46   $166.45   $166.50  
  Purchase #7 $250.33   7.582%   $269.31   $269.31   $269.30   $269.30  
  7 purchase totals = $1,263.53       $1,392.9748   $1,392.97   $1,392.95   $1,393.00