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 $42.53   10.153%   $46.8481   $46.85   $46.85   $46.80  
  Purchase #2 $100.87   5.713%   $106.6327   $106.63   $106.65   $106.60  
  Purchase #3 $201.42   8.625%   $218.7925   $218.79   $218.80   $218.80  
  Purchase #4 $179.77   7.301%   $192.895   $192.90   $192.90   $192.90  
  Purchase #5 $178.86   5.164%   $188.0963   $188.10   $188.10   $188.10  
  Purchase #6 $199.34   7.446%   $214.1829   $214.18   $214.20   $214.20  
  Purchase #7 $93.64   7.392%   $100.5619   $100.56   $100.55   $100.60  
  7 purchase totals = $996.43       $1,068.0094   $1,068.01   $1,068.05   $1,068.00