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 $201.72   5.559%   $212.9336   $212.93   $212.95   $212.90  
  Purchase #2 $93.35   4.518%   $97.5676   $97.57   $97.55   $97.60  
  Purchase #3 $226.62   9.325%   $247.7523   $247.75   $247.75   $247.80  
  Purchase #4 $217.76   6.432%   $231.7663   $231.77   $231.75   $231.80  
  Purchase #5 $227.59   9.329%   $248.8219   $248.82   $248.80   $248.80  
  Purchase #6 $126.59   12.595%   $142.534   $142.53   $142.55   $142.50  
  Purchase #7 $75.58   13.425%   $85.7266   $85.73   $85.75   $85.70  
  7 purchase totals = $1,169.21       $1,267.1023   $1,267.10   $1,267.10   $1,267.10