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 $206.74   5.731%   $218.5883   $218.59   $218.60   $218.60  
  Purchase #2 $93.96   9.262%   $102.6626   $102.66   $102.65   $102.70  
  Purchase #3 $107.68   8.143%   $116.4484   $116.45   $116.45   $116.40  
  Purchase #4 $149.75   8.796%   $162.922   $162.92   $162.90   $162.90  
  Purchase #5 $220.87   7.307%   $237.009   $237.01   $237.00   $237.00  
  Purchase #6 $201.26   9.102%   $219.5787   $219.58   $219.60   $219.60  
  Purchase #7 $119.70   5.582%   $126.3817   $126.38   $126.40   $126.40  
  7 purchase totals = $1,099.96       $1,183.5907   $1,183.59   $1,183.60   $1,183.60