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 $30.47   13.234%   $34.5024   $34.50   $34.50   $34.50  
  Purchase #2 $168.72   12.852%   $190.4039   $190.40   $190.40   $190.40  
  Purchase #3 $106.28   6.678%   $113.3774   $113.38   $113.40   $113.40  
  Purchase #4 $154.30   9.792%   $169.4091   $169.41   $169.40   $169.40  
  Purchase #5 $69.92   6.790%   $74.6676   $74.67   $74.65   $74.70  
  Purchase #6 $213.96   3.864%   $222.2274   $222.23   $222.25   $222.20  
  Purchase #7 $249.54   3.871%   $259.1997   $259.20   $259.20   $259.20  
  7 purchase totals = $993.19       $1,063.7875   $1,063.79   $1,063.80   $1,063.80