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 $63.51   7.138%   $68.0433   $68.04   $68.05   $68.00  
  Purchase #2 $241.78   7.244%   $259.2945   $259.29   $259.30   $259.30  
  Purchase #3 $84.81   9.182%   $92.5973   $92.60   $92.60   $92.60  
  Purchase #4 $107.64   5.321%   $113.3675   $113.37   $113.35   $113.40  
  Purchase #5 $11.49   7.128%   $12.309   $12.31   $12.30   $12.30  
  Purchase #6 $240.35   5.797%   $254.2831   $254.28   $254.30   $254.30  
  Purchase #7 $47.60   12.667%   $53.6295   $53.63   $53.65   $53.60  
  7 purchase totals = $797.18       $853.5242   $853.52   $853.55   $853.50