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 $66.96   5.427%   $70.5939   $70.59   $70.60   $70.60  
  Purchase #2 $62.79   11.179%   $69.8093   $69.81   $69.80   $69.80  
  Purchase #3 $49.76   10.493%   $54.9813   $54.98   $55.00   $55.00  
  Purchase #4 $10.56   5.364%   $11.1264   $11.13   $11.15   $11.10  
  Purchase #5 $41.55   12.226%   $46.6299   $46.63   $46.65   $46.60  
  Purchase #6 $193.68   11.467%   $215.8893   $215.89   $215.90   $215.90  
  Purchase #7 $22.39   11.461%   $24.9561   $24.96   $24.95   $25.00  
  7 purchase totals = $447.69       $493.9862   $493.99   $494.05   $494.00