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 $207.37   13.833%   $236.0555   $236.06   $236.05   $236.10  
  Purchase #2 $222.84   8.584%   $241.9686   $241.97   $241.95   $242.00  
  Purchase #3 $126.99   4.320%   $132.476   $132.48   $132.50   $132.50  
  Purchase #4 $236.36   4.155%   $246.1808   $246.18   $246.20   $246.20  
  Purchase #5 $246.39   4.839%   $258.3128   $258.31   $258.30   $258.30  
  Purchase #6 $141.80   9.485%   $155.2497   $155.25   $155.25   $155.20  
  Purchase #7 $180.31   4.332%   $188.121   $188.12   $188.10   $188.10  
  7 purchase totals = $1,362.06       $1,458.3644   $1,458.37   $1,458.35   $1,458.40