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 $86.51   8.144%   $93.5554   $93.56   $93.55   $93.60  
  Purchase #2 $114.59   4.496%   $119.742   $119.74   $119.75   $119.70  
  Purchase #3 $200.76   8.728%   $218.2823   $218.28   $218.30   $218.30  
  Purchase #4 $150.33   6.611%   $160.2683   $160.27   $160.25   $160.30  
  Purchase #5 $77.45   4.110%   $80.6332   $80.63   $80.65   $80.60  
  Purchase #6 $70.48   5.826%   $74.5862   $74.59   $74.60   $74.60  
  Purchase #7 $189.87   7.118%   $203.3849   $203.38   $203.40   $203.40  
  7 purchase totals = $889.99       $950.4523   $950.45   $950.50   $950.50