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 $87.99   4.558%   $92.0006   $92.00   $92.00   $92.00  
  Purchase #2 $8.43   8.513%   $9.1476   $9.15   $9.15   $9.10  
  Purchase #3 $116.53   13.523%   $132.2884   $132.29   $132.30   $132.30  
  Purchase #4 $149.33   8.730%   $162.3665   $162.37   $162.35   $162.40  
  Purchase #5 $245.75   11.160%   $273.1757   $273.18   $273.20   $273.20  
  Purchase #6 $124.31   8.306%   $134.6352   $134.64   $134.65   $134.60  
  Purchase #7 $53.35   6.448%   $56.79   $56.79   $56.80   $56.80  
  7 purchase totals = $785.69       $860.4040   $860.42   $860.45   $860.40