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 $64.86   13.567%   $73.6596   $73.66   $73.65   $73.70  
  Purchase #2 $92.76   3.102%   $95.6374   $95.64   $95.65   $95.60  
  Purchase #3 $205.46   8.557%   $223.0412   $223.04   $223.05   $223.00  
  Purchase #4 $233.75   6.495%   $248.9321   $248.93   $248.95   $248.90  
  Purchase #5 $71.91   4.552%   $75.1833   $75.18   $75.20   $75.20  
  Purchase #6 $206.79   11.758%   $231.1044   $231.10   $231.10   $231.10  
  Purchase #7 $129.91   12.248%   $145.8214   $145.82   $145.80   $145.80  
  7 purchase totals = $1,005.44       $1,093.3794   $1,093.37   $1,093.40   $1,093.30