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 $56.29   8.482%   $61.0645   $61.06   $61.05   $61.10  
  Purchase #2 $125.79   13.369%   $142.6069   $142.61   $142.60   $142.60  
  Purchase #3 $98.99   10.501%   $109.3849   $109.38   $109.40   $109.40  
  Purchase #4 $125.71   12.611%   $141.5633   $141.56   $141.55   $141.60  
  Purchase #5 $17.61   3.371%   $18.2036   $18.20   $18.20   $18.20  
  Purchase #6 $235.76   13.333%   $267.1939   $267.19   $267.20   $267.20  
  Purchase #7 $41.49   8.372%   $44.9635   $44.96   $44.95   $45.00  
  7 purchase totals = $701.64       $784.9806   $784.96   $784.95   $785.10