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 $186.36   8.172%   $201.5893   $201.59   $201.60   $201.60  
  Purchase #2 $152.49   13.525%   $173.1143   $173.11   $173.10   $173.10  
  Purchase #3 $30.61   11.500%   $34.1302   $34.13   $34.15   $34.10  
  Purchase #4 $163.53   11.205%   $181.8535   $181.85   $181.85   $181.90  
  Purchase #5 $200.77   6.153%   $213.1234   $213.12   $213.10   $213.10  
  Purchase #6 $54.36   6.568%   $57.9304   $57.93   $57.95   $57.90  
  Purchase #7 $58.49   8.276%   $63.3306   $63.33   $63.35   $63.30  
  7 purchase totals = $846.61       $925.0717   $925.06   $925.10   $925.00