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 $170.88   13.499%   $193.9471   $193.95   $193.95   $193.90  
  Purchase #2 $154.46   7.272%   $165.6923   $165.69   $165.70   $165.70  
  Purchase #3 $29.92   12.353%   $33.616   $33.62   $33.60   $33.60  
  Purchase #4 $153.97   6.606%   $164.1413   $164.14   $164.15   $164.10  
  Purchase #5 $219.52   5.574%   $231.756   $231.76   $231.75   $231.80  
  Purchase #6 $63.39   3.515%   $65.6182   $65.62   $65.60   $65.60  
  Purchase #7 $192.39   7.142%   $206.1305   $206.13   $206.15   $206.10  
  7 purchase totals = $984.53       $1,060.9014   $1,060.91   $1,060.90   $1,060.80