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 $95.79   9.253%   $104.6534   $104.65   $104.65   $104.70  
  Purchase #2 $169.57   9.436%   $185.5706   $185.57   $185.55   $185.60  
  Purchase #3 $44.53   3.424%   $46.0547   $46.05   $46.05   $46.10  
  Purchase #4 $25.95   11.177%   $28.8504   $28.85   $28.85   $28.90  
  Purchase #5 $185.90   12.442%   $209.0297   $209.03   $209.05   $209.00  
  Purchase #6 $126.30   12.327%   $141.869   $141.87   $141.85   $141.90  
  Purchase #7 $66.42   8.317%   $71.9442   $71.94   $71.95   $71.90  
  7 purchase totals = $714.46       $787.9720   $787.96   $787.95   $788.10