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 $250.64   5.414%   $264.2096   $264.21   $264.20   $264.20  
  Purchase #2 $107.28   10.642%   $118.6967   $118.70   $118.70   $118.70  
  Purchase #3 $56.85   3.299%   $58.7255   $58.73   $58.75   $58.70  
  Purchase #4 $15.92   7.520%   $17.1172   $17.12   $17.10   $17.10  
  Purchase #5 $192.26   6.231%   $204.2397   $204.24   $204.25   $204.20  
  Purchase #6 $176.43   13.200%   $199.7188   $199.72   $199.70   $199.70  
  Purchase #7 $163.58   13.238%   $185.2347   $185.23   $185.25   $185.20  
  7 purchase totals = $962.96       $1,047.9422   $1,047.95   $1,047.95   $1,047.80