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 $59.98   3.215%   $61.9084   $61.91   $61.90   $61.90  
  Purchase #2 $248.32   9.380%   $271.6124   $271.61   $271.60   $271.60  
  Purchase #3 $96.53   7.283%   $103.5603   $103.56   $103.55   $103.60  
  Purchase #4 $79.93   9.471%   $87.5002   $87.50   $87.50   $87.50  
  Purchase #5 $204.25   13.177%   $231.164   $231.16   $231.15   $231.20  
  Purchase #6 $114.96   9.191%   $125.526   $125.53   $125.55   $125.50  
  Purchase #7 $23.56   9.702%   $25.8458   $25.85   $25.85   $25.80  
  7 purchase totals = $827.53       $907.1171   $907.12   $907.10   $907.10