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 $241.86   10.778%   $267.9277   $267.93   $267.95   $267.90  
  Purchase #2 $109.74   13.565%   $124.6262   $124.63   $124.65   $124.60  
  Purchase #3 $234.92   6.577%   $250.3707   $250.37   $250.35   $250.40  
  Purchase #4 $98.31   13.560%   $111.6408   $111.64   $111.65   $111.60  
  Purchase #5 $46.34   6.310%   $49.2641   $49.26   $49.25   $49.30  
  Purchase #6 $50.58   12.430%   $56.8671   $56.87   $56.85   $56.90  
  Purchase #7 $157.83   7.276%   $169.3137   $169.31   $169.30   $169.30  
  7 purchase totals = $939.58       $1,030.0103   $1,030.01   $1,030.00   $1,030.00