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 $244.25   8.218%   $264.3225   $264.32   $264.30   $264.30  
  Purchase #2 $179.89   7.214%   $192.8673   $192.87   $192.85   $192.90  
  Purchase #3 $248.30   8.865%   $270.3118   $270.31   $270.30   $270.30  
  Purchase #4 $46.84   8.752%   $50.9394   $50.94   $50.95   $50.90  
  Purchase #5 $149.36   11.102%   $165.9419   $165.94   $165.95   $165.90  
  Purchase #6 $196.86   6.766%   $210.1795   $210.18   $210.20   $210.20  
  Purchase #7 $5.88   5.269%   $6.1898   $6.19   $6.20   $6.20  
  7 purchase totals = $1,071.38       $1,160.7522   $1,160.75   $1,160.75   $1,160.70