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 $181.95   8.641%   $197.6723   $197.67   $197.65   $197.70  
  Purchase #2 $53.62   12.644%   $60.3997   $60.40   $60.40   $60.40  
  Purchase #3 $80.53   3.147%   $83.0643   $83.06   $83.05   $83.10  
  Purchase #4 $162.32   4.468%   $169.5725   $169.57   $169.55   $169.60  
  Purchase #5 $74.90   13.365%   $84.9104   $84.91   $84.90   $84.90  
  Purchase #6 $206.53   12.822%   $233.0113   $233.01   $233.00   $233.00  
  Purchase #7 $129.56   6.190%   $137.5798   $137.58   $137.60   $137.60  
  7 purchase totals = $889.41       $966.2103   $966.20   $966.15   $966.30