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 $53.85   12.488%   $60.5748   $60.57   $60.55   $60.60  
  Purchase #2 $131.25   7.223%   $140.7302   $140.73   $140.75   $140.70  
  Purchase #3 $36.94   12.653%   $41.614   $41.61   $41.60   $41.60  
  Purchase #4 $117.27   10.373%   $129.4344   $129.43   $129.45   $129.40  
  Purchase #5 $98.58   5.174%   $103.6805   $103.68   $103.70   $103.70  
  Purchase #6 $56.80   9.380%   $62.1278   $62.13   $62.15   $62.10  
  Purchase #7 $202.41   13.287%   $229.3042   $229.30   $229.30   $229.30  
  7 purchase totals = $697.10       $767.4659   $767.45   $767.50   $767.40