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 $90.92   4.794%   $95.2787   $95.28   $95.30   $95.30  
  Purchase #2 $10.41   8.200%   $11.2636   $11.26   $11.25   $11.30  
  Purchase #3 $183.27   9.828%   $201.2818   $201.28   $201.30   $201.30  
  Purchase #4 $241.81   10.830%   $267.998   $268.00   $268.00   $268.00  
  Purchase #5 $98.37   8.108%   $106.3458   $106.35   $106.35   $106.30  
  Purchase #6 $157.55   5.662%   $166.4705   $166.47   $166.45   $166.50  
  Purchase #7 $7.82   4.784%   $8.1941   $8.19   $8.20   $8.20  
  7 purchase totals = $790.15       $856.8325   $856.83   $856.85   $856.90