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 $188.79   13.456%   $214.1936   $214.19   $214.20   $214.20  
  Purchase #2 $95.31   4.669%   $99.76   $99.76   $99.75   $99.80  
  Purchase #3 $34.67   8.120%   $37.4852   $37.49   $37.50   $37.50  
  Purchase #4 $193.33   8.484%   $209.7321   $209.73   $209.75   $209.70  
  Purchase #5 $203.58   4.221%   $212.1731   $212.17   $212.15   $212.20  
  Purchase #6 $165.99   8.591%   $180.2502   $180.25   $180.25   $180.30  
  Purchase #7 $52.45   8.431%   $56.8721   $56.87   $56.85   $56.90  
  7 purchase totals = $934.12       $1,010.4663   $1,010.46   $1,010.45   $1,010.60