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 $61.82   6.696%   $65.9595   $65.96   $65.95   $66.00  
  Purchase #2 $83.83   5.758%   $88.6569   $88.66   $88.65   $88.70  
  Purchase #3 $211.35   7.338%   $226.8589   $226.86   $226.85   $226.90  
  Purchase #4 $140.77   6.185%   $149.4766   $149.48   $149.50   $149.50  
  Purchase #5 $221.99   8.287%   $240.3863   $240.39   $240.40   $240.40  
  Purchase #6 $169.68   13.574%   $192.7124   $192.71   $192.70   $192.70  
  Purchase #7 $151.25   5.206%   $159.1241   $159.12   $159.10   $159.10  
  7 purchase totals = $1,040.69       $1,123.1747   $1,123.18   $1,123.15   $1,123.30