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 $168.98   10.561%   $186.826   $186.83   $186.85   $186.80  
  Purchase #2 $194.37   4.298%   $202.724   $202.72   $202.70   $202.70  
  Purchase #3 $48.82   4.449%   $50.992   $50.99   $51.00   $51.00  
  Purchase #4 $168.81   11.586%   $188.3683   $188.37   $188.35   $188.40  
  Purchase #5 $43.97   9.661%   $48.2179   $48.22   $48.20   $48.20  
  Purchase #6 $55.85   12.749%   $62.9703   $62.97   $62.95   $63.00  
  Purchase #7 $122.25   6.134%   $129.7488   $129.75   $129.75   $129.70  
  7 purchase totals = $803.05       $869.8473   $869.85   $869.80   $869.80