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 $202.99   11.804%   $226.9509   $226.95   $226.95   $227.00  
  Purchase #2 $126.79   8.463%   $137.5202   $137.52   $137.50   $137.50  
  Purchase #3 $98.32   8.479%   $106.6566   $106.66   $106.65   $106.70  
  Purchase #4 $23.31   5.222%   $24.5272   $24.53   $24.55   $24.50  
  Purchase #5 $119.80   11.149%   $133.1565   $133.16   $133.15   $133.20  
  Purchase #6 $90.64   11.671%   $101.2186   $101.22   $101.20   $101.20  
  Purchase #7 $130.69   7.365%   $140.3153   $140.32   $140.30   $140.30  
  7 purchase totals = $792.54       $870.3453   $870.36   $870.30   $870.40