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 $86.98   12.767%   $98.0847   $98.08   $98.10   $98.10  
  Purchase #2 $175.78   5.182%   $184.8889   $184.89   $184.90   $184.90  
  Purchase #3 $183.48   5.801%   $194.1237   $194.12   $194.10   $194.10  
  Purchase #4 $83.89   8.557%   $91.0685   $91.07   $91.05   $91.10  
  Purchase #5 $125.27   6.760%   $133.7383   $133.74   $133.75   $133.70  
  Purchase #6 $249.87   8.815%   $271.896   $271.90   $271.90   $271.90  
  Purchase #7 $157.75   8.307%   $170.8543   $170.85   $170.85   $170.90  
  7 purchase totals = $1,063.02       $1,144.6544   $1,144.65   $1,144.65   $1,144.70