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 $180.51   10.566%   $199.5827   $199.58   $199.60   $199.60  
  Purchase #2 $177.48   8.606%   $192.7539   $192.75   $192.75   $192.80  
  Purchase #3 $219.43   8.147%   $237.307   $237.31   $237.30   $237.30  
  Purchase #4 $42.33   11.705%   $47.2847   $47.28   $47.30   $47.30  
  Purchase #5 $32.86   5.163%   $34.5566   $34.56   $34.55   $34.60  
  Purchase #6 $184.77   5.535%   $194.997   $195.00   $195.00   $195.00  
  Purchase #7 $65.96   9.637%   $72.3166   $72.32   $72.30   $72.30  
  7 purchase totals = $903.34       $978.7985   $978.80   $978.80   $978.90