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 $162.71   3.148%   $167.8321   $167.83   $167.85   $167.80  
  Purchase #2 $38.34   8.365%   $41.5471   $41.55   $41.55   $41.50  
  Purchase #3 $151.65   5.238%   $159.5934   $159.59   $159.60   $159.60  
  Purchase #4 $68.89   7.297%   $73.9169   $73.92   $73.90   $73.90  
  Purchase #5 $111.99   11.202%   $124.5351   $124.54   $124.55   $124.50  
  Purchase #6 $106.69   11.155%   $118.5913   $118.59   $118.60   $118.60  
  Purchase #7 $145.37   7.112%   $155.7087   $155.71   $155.70   $155.70  
  7 purchase totals = $785.64       $841.7246   $841.73   $841.75   $841.60