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 $231.60   12.118%   $259.6653   $259.67   $259.65   $259.70  
  Purchase #2 $226.70   5.301%   $238.7174   $238.72   $238.70   $238.70  
  Purchase #3 $216.39   3.752%   $224.509   $224.51   $224.50   $224.50  
  Purchase #4 $160.75   5.113%   $168.9691   $168.97   $168.95   $169.00  
  Purchase #5 $98.27   11.402%   $109.4747   $109.47   $109.45   $109.50  
  Purchase #6 $151.59   8.255%   $164.1038   $164.10   $164.10   $164.10  
  Purchase #7 $118.67   3.502%   $122.8258   $122.83   $122.85   $122.80  
  7 purchase totals = $1,203.97       $1,288.2651   $1,288.27   $1,288.20   $1,288.30