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 $170.61   7.838%   $183.9824   $183.98   $184.00   $184.00  
  Purchase #2 $226.61   4.196%   $236.1186   $236.12   $236.10   $236.10  
  Purchase #3 $26.94   8.300%   $29.176   $29.18   $29.20   $29.20  
  Purchase #4 $53.72   3.492%   $55.5959   $55.60   $55.60   $55.60  
  Purchase #5 $41.61   6.421%   $44.2818   $44.28   $44.30   $44.30  
  Purchase #6 $5.73   6.269%   $6.0892   $6.09   $6.10   $6.10  
  Purchase #7 $37.85   3.609%   $39.216   $39.22   $39.20   $39.20  
  7 purchase totals = $563.07       $594.4599   $594.47   $594.50   $594.50