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 $111.36   12.737%   $125.5439   $125.54   $125.55   $125.50  
  Purchase #2 $160.98   3.717%   $166.9636   $166.96   $166.95   $167.00  
  Purchase #3 $34.34   6.786%   $36.6703   $36.67   $36.65   $36.70  
  Purchase #4 $206.49   6.670%   $220.2629   $220.26   $220.25   $220.30  
  Purchase #5 $119.86   9.852%   $131.6686   $131.67   $131.65   $131.70  
  Purchase #6 $136.39   11.416%   $151.9603   $151.96   $151.95   $152.00  
  Purchase #7 $67.87   10.627%   $75.0825   $75.08   $75.10   $75.10  
  7 purchase totals = $837.29       $908.1521   $908.14   $908.10   $908.30