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 $84.96   8.490%   $92.1731   $92.17   $92.15   $92.20  
  Purchase #2 $96.38   6.840%   $102.9724   $102.97   $102.95   $103.00  
  Purchase #3 $18.96   5.367%   $19.9776   $19.98   $20.00   $20.00  
  Purchase #4 $245.91   6.667%   $262.3048   $262.30   $262.30   $262.30  
  Purchase #5 $222.79   4.493%   $232.8   $232.80   $232.80   $232.80  
  Purchase #6 $129.58   9.535%   $141.9355   $141.94   $141.95   $141.90  
  Purchase #7 $149.45   8.750%   $162.5269   $162.53   $162.55   $162.50  
  7 purchase totals = $948.03       $1,014.6903   $1,014.69   $1,014.70   $1,014.70