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 $65.36   10.341%   $72.1189   $72.12   $72.10   $72.10  
  Purchase #2 $223.57   7.305%   $239.9018   $239.90   $239.90   $239.90  
  Purchase #3 $168.26   11.813%   $188.1366   $188.14   $188.15   $188.10  
  Purchase #4 $119.94   9.719%   $131.597   $131.60   $131.60   $131.60  
  Purchase #5 $129.39   3.707%   $134.1865   $134.19   $134.20   $134.20  
  Purchase #6 $200.39   10.771%   $221.974   $221.97   $221.95   $222.00  
  Purchase #7 $33.74   5.148%   $35.4769   $35.48   $35.50   $35.50  
  7 purchase totals = $940.65       $1,023.3917   $1,023.40   $1,023.40   $1,023.40