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 $176.55   9.832%   $193.9084   $193.91   $193.90   $193.90  
  Purchase #2 $235.39   6.786%   $251.3636   $251.36   $251.35   $251.40  
  Purchase #3 $158.29   11.617%   $176.6785   $176.68   $176.70   $176.70  
  Purchase #4 $19.99   13.285%   $22.6457   $22.65   $22.65   $22.60  
  Purchase #5 $125.52   11.537%   $140.0012   $140.00   $140.00   $140.00  
  Purchase #6 $132.91   12.116%   $149.0134   $149.01   $149.00   $149.00  
  Purchase #7 $67.39   11.796%   $75.3393   $75.34   $75.35   $75.30  
  7 purchase totals = $916.04       $1,008.9501   $1,008.95   $1,008.95   $1,008.90