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 $186.55   8.427%   $202.2706   $202.27   $202.25   $202.30  
  Purchase #2 $61.74   8.836%   $67.1953   $67.20   $67.20   $67.20  
  Purchase #3 $105.29   4.161%   $109.6711   $109.67   $109.65   $109.70  
  Purchase #4 $212.71   6.102%   $225.6896   $225.69   $225.70   $225.70  
  Purchase #5 $108.86   10.473%   $120.2609   $120.26   $120.25   $120.30  
  Purchase #6 $11.51   6.811%   $12.2939   $12.29   $12.30   $12.30  
  Purchase #7 $178.82   5.745%   $189.0932   $189.09   $189.10   $189.10  
  7 purchase totals = $865.48       $926.4746   $926.47   $926.45   $926.60