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 $168.76   8.502%   $183.108   $183.11   $183.10   $183.10  
  Purchase #2 $106.75   11.294%   $118.8063   $118.81   $118.80   $118.80  
  Purchase #3 $53.51   4.615%   $55.9795   $55.98   $56.00   $56.00  
  Purchase #4 $173.69   5.338%   $182.9616   $182.96   $182.95   $183.00  
  Purchase #5 $140.58   7.275%   $150.8072   $150.81   $150.80   $150.80  
  Purchase #6 $55.57   11.831%   $62.1445   $62.14   $62.15   $62.10  
  Purchase #7 $71.81   13.393%   $81.4275   $81.43   $81.45   $81.40  
  7 purchase totals = $770.67       $835.2346   $835.24   $835.25   $835.20