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 $186.77   8.764%   $203.1385   $203.14   $203.15   $203.10  
  Purchase #2 $222.27   8.724%   $241.6608   $241.66   $241.65   $241.70  
  Purchase #3 $117.88   3.529%   $122.04   $122.04   $122.05   $122.00  
  Purchase #4 $167.79   8.303%   $181.7216   $181.72   $181.70   $181.70  
  Purchase #5 $120.81   3.706%   $125.2872   $125.29   $125.30   $125.30  
  Purchase #6 $132.50   4.667%   $138.6838   $138.68   $138.70   $138.70  
  Purchase #7 $185.85   3.153%   $191.7099   $191.71   $191.70   $191.70  
  7 purchase totals = $1,133.87       $1,204.2418   $1,204.24   $1,204.25   $1,204.20