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 $67.46   5.403%   $71.1049   $71.10   $71.10   $71.10  
  Purchase #2 $201.66   11.586%   $225.0243   $225.02   $225.00   $225.00  
  Purchase #3 $81.79   8.272%   $88.5557   $88.56   $88.55   $88.60  
  Purchase #4 $248.64   6.748%   $265.4182   $265.42   $265.40   $265.40  
  Purchase #5 $75.74   5.835%   $80.1594   $80.16   $80.15   $80.20  
  Purchase #6 $38.69   6.720%   $41.29   $41.29   $41.30   $41.30  
  Purchase #7 $139.70   10.688%   $154.6311   $154.63   $154.65   $154.60  
  7 purchase totals = $853.68       $926.1836   $926.18   $926.15   $926.20