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 $214.48   10.437%   $236.8653   $236.87   $236.85   $236.90  
  Purchase #2 $6.93   7.447%   $7.4461   $7.45   $7.45   $7.40  
  Purchase #3 $179.44   3.729%   $186.1313   $186.13   $186.15   $186.10  
  Purchase #4 $165.99   9.163%   $181.1997   $181.20   $181.20   $181.20  
  Purchase #5 $201.92   13.229%   $228.632   $228.63   $228.65   $228.60  
  Purchase #6 $152.63   3.706%   $158.2865   $158.29   $158.30   $158.30  
  Purchase #7 $8.78   12.344%   $9.8638   $9.86   $9.85   $9.90  
  7 purchase totals = $930.17       $1,008.4247   $1,008.43   $1,008.45   $1,008.40