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 $60.84   13.470%   $69.0351   $69.04   $69.05   $69.00  
  Purchase #2 $75.40   4.497%   $78.7907   $78.79   $78.80   $78.80  
  Purchase #3 $136.26   13.302%   $154.3853   $154.39   $154.40   $154.40  
  Purchase #4 $177.65   12.144%   $199.2238   $199.22   $199.20   $199.20  
  Purchase #5 $213.96   8.854%   $232.904   $232.90   $232.90   $232.90  
  Purchase #6 $148.76   8.120%   $160.8393   $160.84   $160.85   $160.80  
  Purchase #7 $157.58   11.840%   $176.2375   $176.24   $176.25   $176.20  
  7 purchase totals = $970.45       $1,071.4157   $1,071.42   $1,071.45   $1,071.30