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 $154.49   7.241%   $165.6766   $165.68   $165.70   $165.70  
  Purchase #2 $150.36   7.745%   $162.0054   $162.01   $162.00   $162.00  
  Purchase #3 $78.68   7.376%   $84.4834   $84.48   $84.50   $84.50  
  Purchase #4 $208.26   9.402%   $227.8406   $227.84   $227.85   $227.80  
  Purchase #5 $200.99   8.132%   $217.3345   $217.33   $217.35   $217.30  
  Purchase #6 $116.37   10.613%   $128.7203   $128.72   $128.70   $128.70  
  Purchase #7 $246.96   4.407%   $257.8435   $257.84   $257.85   $257.80  
  7 purchase totals = $1,156.11       $1,243.9043   $1,243.90   $1,243.95   $1,243.80