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 $54.71   10.794%   $60.6154   $60.62   $60.60   $60.60  
  Purchase #2 $14.64   9.550%   $16.0381   $16.04   $16.05   $16.00  
  Purchase #3 $115.98   9.616%   $127.1326   $127.13   $127.15   $127.10  
  Purchase #4 $180.82   7.418%   $194.2332   $194.23   $194.25   $194.20  
  Purchase #5 $162.90   11.354%   $181.3957   $181.40   $181.40   $181.40  
  Purchase #6 $162.47   11.780%   $181.609   $181.61   $181.60   $181.60  
  Purchase #7 $47.27   13.427%   $53.6169   $53.62   $53.60   $53.60  
  7 purchase totals = $738.79       $814.6409   $814.65   $814.65   $814.50