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 $113.64   11.675%   $126.9075   $126.91   $126.90   $126.90  
  Purchase #2 $18.61   4.505%   $19.4484   $19.45   $19.45   $19.40  
  Purchase #3 $194.50   4.280%   $202.8246   $202.82   $202.80   $202.80  
  Purchase #4 $58.51   4.751%   $61.2898   $61.29   $61.30   $61.30  
  Purchase #5 $137.72   6.162%   $146.2063   $146.21   $146.20   $146.20  
  Purchase #6 $181.99   12.685%   $205.0754   $205.08   $205.10   $205.10  
  Purchase #7 $69.66   7.430%   $74.8357   $74.84   $74.85   $74.80  
  7 purchase totals = $774.63       $836.5877   $836.60   $836.60   $836.50