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 $194.39   6.129%   $206.3042   $206.30   $206.30   $206.30  
  Purchase #2 $62.95   6.443%   $67.0059   $67.01   $67.00   $67.00  
  Purchase #3 $62.74   5.316%   $66.0753   $66.08   $66.10   $66.10  
  Purchase #4 $142.40   13.555%   $161.7023   $161.70   $161.70   $161.70  
  Purchase #5 $21.30   7.541%   $22.9062   $22.91   $22.90   $22.90  
  Purchase #6 $250.83   7.590%   $269.868   $269.87   $269.85   $269.90  
  Purchase #7 $241.53   4.328%   $251.9834   $251.98   $252.00   $252.00  
  7 purchase totals = $976.14       $1,045.8453   $1,045.85   $1,045.85   $1,045.90