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 $237.51   6.846%   $253.7699   $253.77   $253.75   $253.80  
  Purchase #2 $7.58   9.837%   $8.3256   $8.33   $8.35   $8.30  
  Purchase #3 $64.33   7.860%   $69.3863   $69.39   $69.40   $69.40  
  Purchase #4 $89.67   4.180%   $93.4182   $93.42   $93.40   $93.40  
  Purchase #5 $235.92   5.824%   $249.66   $249.66   $249.65   $249.70  
  Purchase #6 $215.50   3.488%   $223.0166   $223.02   $223.00   $223.00  
  Purchase #7 $9.27   11.867%   $10.3701   $10.37   $10.35   $10.40  
  7 purchase totals = $859.78       $907.9467   $907.96   $907.90   $908.00