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 $59.54   8.254%   $64.4544   $64.45   $64.45   $64.50  
  Purchase #2 $241.89   6.870%   $258.5078   $258.51   $258.50   $258.50  
  Purchase #3 $154.65   7.572%   $166.3601   $166.36   $166.35   $166.40  
  Purchase #4 $245.97   6.872%   $262.8731   $262.87   $262.85   $262.90  
  Purchase #5 $69.42   9.566%   $76.0607   $76.06   $76.05   $76.10  
  Purchase #6 $130.88   5.185%   $137.6661   $137.67   $137.65   $137.70  
  Purchase #7 $190.54   5.469%   $200.9606   $200.96   $200.95   $201.00  
  7 purchase totals = $1,092.89       $1,166.8828   $1,166.88   $1,166.80   $1,167.10