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 $243.32   9.839%   $267.2603   $267.26   $267.25   $267.30  
  Purchase #2 $11.25   4.300%   $11.7338   $11.73   $11.75   $11.70  
  Purchase #3 $120.84   9.577%   $132.4128   $132.41   $132.40   $132.40  
  Purchase #4 $103.43   6.859%   $110.5243   $110.52   $110.50   $110.50  
  Purchase #5 $209.35   13.844%   $238.3324   $238.33   $238.35   $238.30  
  Purchase #6 $146.86   7.794%   $158.3063   $158.31   $158.30   $158.30  
  Purchase #7 $83.99   5.261%   $88.4087   $88.41   $88.40   $88.40  
  7 purchase totals = $919.04       $1,006.9786   $1,006.97   $1,006.95   $1,006.90