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 $87.78   8.830%   $95.531   $95.53   $95.55   $95.50  
  Purchase #2 $10.77   9.798%   $11.8252   $11.83   $11.85   $11.80  
  Purchase #3 $91.93   11.669%   $102.6573   $102.66   $102.65   $102.70  
  Purchase #4 $205.91   3.645%   $213.4154   $213.42   $213.40   $213.40  
  Purchase #5 $158.56   11.531%   $176.8436   $176.84   $176.85   $176.80  
  Purchase #6 $75.91   11.358%   $84.5319   $84.53   $84.55   $84.50  
  Purchase #7 $20.28   9.706%   $22.2484   $22.25   $22.25   $22.20  
  7 purchase totals = $651.14       $707.0528   $707.06   $707.10   $706.90