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 $168.53   13.486%   $191.258   $191.26   $191.25   $191.30  
  Purchase #2 $31.43   5.744%   $33.2353   $33.24   $33.25   $33.20  
  Purchase #3 $210.27   12.651%   $236.8713   $236.87   $236.85   $236.90  
  Purchase #4 $145.90   11.627%   $162.8638   $162.86   $162.85   $162.90  
  Purchase #5 $173.64   6.115%   $184.2581   $184.26   $184.25   $184.30  
  Purchase #6 $199.29   4.278%   $207.8156   $207.82   $207.80   $207.80  
  Purchase #7 $237.88   4.744%   $249.165   $249.17   $249.15   $249.20  
  7 purchase totals = $1,166.94       $1,265.4671   $1,265.48   $1,265.40   $1,265.60