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 $250.73   6.732%   $267.6091   $267.61   $267.60   $267.60  
  Purchase #2 $5.90   11.309%   $6.5672   $6.57   $6.55   $6.60  
  Purchase #3 $114.29   13.119%   $129.2837   $129.28   $129.30   $129.30  
  Purchase #4 $22.95   10.401%   $25.337   $25.34   $25.35   $25.30  
  Purchase #5 $215.55   8.190%   $233.2035   $233.20   $233.20   $233.20  
  Purchase #6 $207.74   12.447%   $233.5974   $233.60   $233.60   $233.60  
  Purchase #7 $141.64   9.728%   $155.4187   $155.42   $155.40   $155.40  
  7 purchase totals = $958.80       $1,051.0166   $1,051.02   $1,051.00   $1,051.00