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 $175.96   6.129%   $186.7446   $186.74   $186.75   $186.70  
  Purchase #2 $226.89   6.859%   $242.4524   $242.45   $242.45   $242.50  
  Purchase #3 $228.35   7.590%   $245.6818   $245.68   $245.70   $245.70  
  Purchase #4 $66.86   12.803%   $75.4201   $75.42   $75.40   $75.40  
  Purchase #5 $52.72   5.137%   $55.4282   $55.43   $55.45   $55.40  
  Purchase #6 $48.57   11.394%   $54.1041   $54.10   $54.10   $54.10  
  Purchase #7 $192.43   5.724%   $203.4447   $203.44   $203.45   $203.40  
  7 purchase totals = $991.78       $1,063.2759   $1,063.26   $1,063.30   $1,063.20