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 $68.95   10.720%   $76.3414   $76.34   $76.35   $76.30  
  Purchase #2 $74.35   6.698%   $79.33   $79.33   $79.35   $79.30  
  Purchase #3 $107.43   8.447%   $116.5046   $116.50   $116.50   $116.50  
  Purchase #4 $197.96   5.471%   $208.7904   $208.79   $208.80   $208.80  
  Purchase #5 $73.51   13.107%   $83.145   $83.15   $83.15   $83.10  
  Purchase #6 $180.32   10.731%   $199.6701   $199.67   $199.65   $199.70  
  Purchase #7 $141.66   3.868%   $147.1394   $147.14   $147.15   $147.10  
  7 purchase totals = $844.18       $910.9209   $910.92   $910.95   $910.80