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 $235.62   13.596%   $267.6549   $267.65   $267.65   $267.70  
  Purchase #2 $196.26   6.414%   $208.8481   $208.85   $208.85   $208.80  
  Purchase #3 $68.29   7.262%   $73.2492   $73.25   $73.25   $73.20  
  Purchase #4 $120.82   4.278%   $125.9887   $125.99   $126.00   $126.00  
  Purchase #5 $202.52   10.874%   $224.542   $224.54   $224.55   $224.50  
  Purchase #6 $165.25   12.680%   $186.2037   $186.20   $186.20   $186.20  
  Purchase #7 $205.68   13.505%   $233.4571   $233.46   $233.45   $233.50  
  7 purchase totals = $1,194.44       $1,319.9437   $1,319.94   $1,319.95   $1,319.90