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 $183.66   8.489%   $199.2509   $199.25   $199.25   $199.30  
  Purchase #2 $214.77   12.663%   $241.9663   $241.97   $241.95   $242.00  
  Purchase #3 $127.73   6.418%   $135.9277   $135.93   $135.95   $135.90  
  Purchase #4 $172.65   12.366%   $193.9999   $194.00   $194.00   $194.00  
  Purchase #5 $150.50   12.388%   $169.1439   $169.14   $169.15   $169.10  
  Purchase #6 $54.33   11.845%   $60.7654   $60.77   $60.75   $60.80  
  Purchase #7 $212.90   9.418%   $232.9509   $232.95   $232.95   $233.00  
  7 purchase totals = $1,116.54       $1,234.0050   $1,234.01   $1,234.00   $1,234.10