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 $42.96   7.734%   $46.2825   $46.28   $46.30   $46.30  
  Purchase #2 $231.65   10.750%   $256.5524   $256.55   $256.55   $256.60  
  Purchase #3 $201.97   4.771%   $211.606   $211.61   $211.60   $211.60  
  Purchase #4 $227.43   7.634%   $244.792   $244.79   $244.80   $244.80  
  Purchase #5 $195.42   3.639%   $202.5313   $202.53   $202.55   $202.50  
  Purchase #6 $181.80   5.440%   $191.6899   $191.69   $191.70   $191.70  
  Purchase #7 $68.62   3.454%   $70.9901   $70.99   $71.00   $71.00  
  7 purchase totals = $1,149.85       $1,224.4442   $1,224.44   $1,224.50   $1,224.50