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 $96.33   11.244%   $107.1613   $107.16   $107.15   $107.20  
  Purchase #2 $50.65   5.349%   $53.3593   $53.36   $53.35   $53.40  
  Purchase #3 $141.27   11.866%   $158.0331   $158.03   $158.05   $158.00  
  Purchase #4 $176.57   6.395%   $187.8617   $187.86   $187.85   $187.90  
  Purchase #5 $56.40   12.522%   $63.4624   $63.46   $63.45   $63.50  
  Purchase #6 $124.96   11.587%   $139.4391   $139.44   $139.45   $139.40  
  Purchase #7 $128.33   11.178%   $142.6747   $142.67   $142.65   $142.70  
  7 purchase totals = $774.51       $851.9916   $851.98   $851.95   $852.10