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 $176.47   10.374%   $194.777   $194.78   $194.80   $194.80  
  Purchase #2 $5.36   10.210%   $5.9073   $5.91   $5.90   $5.90  
  Purchase #3 $76.37   7.279%   $81.929   $81.93   $81.95   $81.90  
  Purchase #4 $172.53   8.198%   $186.674   $186.67   $186.65   $186.70  
  Purchase #5 $88.79   11.392%   $98.905   $98.91   $98.90   $98.90  
  Purchase #6 $161.28   10.820%   $178.7305   $178.73   $178.75   $178.70  
  Purchase #7 $156.65   12.154%   $175.6892   $175.69   $175.70   $175.70  
  7 purchase totals = $837.45       $922.6120   $922.62   $922.65   $922.60