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 $61.97   9.369%   $67.776   $67.78   $67.80   $67.80  
  Purchase #2 $191.99   12.734%   $216.438   $216.44   $216.45   $216.40  
  Purchase #3 $213.99   10.440%   $236.3306   $236.33   $236.35   $236.30  
  Purchase #4 $166.34   6.745%   $177.5596   $177.56   $177.55   $177.60  
  Purchase #5 $140.92   4.675%   $147.508   $147.51   $147.50   $147.50  
  Purchase #6 $34.92   13.748%   $39.7208   $39.72   $39.70   $39.70  
  Purchase #7 $93.51   4.834%   $98.0303   $98.03   $98.05   $98.00  
  7 purchase totals = $903.64       $983.3633   $983.37   $983.40   $983.30