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 $179.85   9.147%   $196.3009   $196.30   $196.30   $196.30  
  Purchase #2 $53.54   4.352%   $55.8701   $55.87   $55.85   $55.90  
  Purchase #3 $219.64   3.199%   $226.6663   $226.67   $226.65   $226.70  
  Purchase #4 $250.39   5.220%   $263.4604   $263.46   $263.45   $263.50  
  Purchase #5 $103.69   12.634%   $116.7902   $116.79   $116.80   $116.80  
  Purchase #6 $122.89   5.671%   $129.8591   $129.86   $129.85   $129.90  
  Purchase #7 $192.91   6.603%   $205.6478   $205.65   $205.65   $205.60  
  7 purchase totals = $1,122.91       $1,194.5948   $1,194.60   $1,194.55   $1,194.70