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 $106.76   11.762%   $119.3171   $119.32   $119.30   $119.30  
  Purchase #2 $202.59   3.495%   $209.6705   $209.67   $209.65   $209.70  
  Purchase #3 $34.70   4.716%   $36.3365   $36.34   $36.35   $36.30  
  Purchase #4 $192.25   10.756%   $212.9284   $212.93   $212.95   $212.90  
  Purchase #5 $125.90   5.540%   $132.8749   $132.87   $132.85   $132.90  
  Purchase #6 $182.74   7.356%   $196.1824   $196.18   $196.20   $196.20  
  Purchase #7 $33.30   4.692%   $34.8624   $34.86   $34.85   $34.90  
  7 purchase totals = $878.24       $942.1722   $942.17   $942.15   $942.20