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 $224.47   9.624%   $246.073   $246.07   $246.05   $246.10  
  Purchase #2 $62.29   8.473%   $67.5678   $67.57   $67.55   $67.60  
  Purchase #3 $191.58   10.492%   $211.6806   $211.68   $211.70   $211.70  
  Purchase #4 $47.27   7.513%   $50.8214   $50.82   $50.80   $50.80  
  Purchase #5 $210.81   4.664%   $220.6422   $220.64   $220.65   $220.60  
  Purchase #6 $35.33   5.579%   $37.3011   $37.30   $37.30   $37.30  
  Purchase #7 $11.44   4.872%   $11.9974   $12.00   $12.00   $12.00  
  7 purchase totals = $783.19       $846.0835   $846.08   $846.05   $846.10