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 $32.93   11.757%   $36.8016   $36.80   $36.80   $36.80  
  Purchase #2 $126.87   7.434%   $136.3015   $136.30   $136.30   $136.30  
  Purchase #3 $133.56   7.501%   $143.5783   $143.58   $143.60   $143.60  
  Purchase #4 $131.76   5.259%   $138.6893   $138.69   $138.70   $138.70  
  Purchase #5 $145.54   4.162%   $151.5974   $151.60   $151.60   $151.60  
  Purchase #6 $27.85   4.122%   $28.998   $29.00   $29.00   $29.00  
  Purchase #7 $119.68   13.294%   $135.5903   $135.59   $135.60   $135.60  
  7 purchase totals = $718.19       $771.5564   $771.56   $771.60   $771.60