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 $61.37   9.196%   $67.0136   $67.01   $67.00   $67.00  
  Purchase #2 $193.34   13.609%   $219.6516   $219.65   $219.65   $219.70  
  Purchase #3 $159.33   11.643%   $177.8808   $177.88   $177.90   $177.90  
  Purchase #4 $193.36   8.304%   $209.4166   $209.42   $209.40   $209.40  
  Purchase #5 $102.70   9.205%   $112.1535   $112.15   $112.15   $112.20  
  Purchase #6 $177.51   12.459%   $199.626   $199.63   $199.65   $199.60  
  Purchase #7 $78.49   9.452%   $85.9089   $85.91   $85.90   $85.90  
  7 purchase totals = $966.10       $1,071.6510   $1,071.65   $1,071.65   $1,071.70