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 $171.57   6.499%   $182.7203   $182.72   $182.70   $182.70  
  Purchase #2 $57.71   12.635%   $65.0017   $65.00   $65.00   $65.00  
  Purchase #3 $165.86   12.840%   $187.1564   $187.16   $187.15   $187.20  
  Purchase #4 $84.85   10.827%   $94.0367   $94.04   $94.05   $94.00  
  Purchase #5 $14.83   10.834%   $16.4367   $16.44   $16.45   $16.40  
  Purchase #6 $204.87   3.149%   $211.3214   $211.32   $211.30   $211.30  
  Purchase #7 $75.81   11.763%   $84.7275   $84.73   $84.75   $84.70  
  7 purchase totals = $775.50       $841.4007   $841.41   $841.40   $841.30