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 $35.88   6.490%   $38.2086   $38.21   $38.20   $38.20  
  Purchase #2 $84.75   11.544%   $94.5335   $94.53   $94.55   $94.50  
  Purchase #3 $59.35   3.143%   $61.2154   $61.22   $61.20   $61.20  
  Purchase #4 $179.79   9.639%   $197.12   $197.12   $197.10   $197.10  
  Purchase #5 $115.85   6.578%   $123.4706   $123.47   $123.45   $123.50  
  Purchase #6 $181.50   3.216%   $187.337   $187.34   $187.35   $187.30  
  Purchase #7 $28.27   7.492%   $30.388   $30.39   $30.40   $30.40  
  7 purchase totals = $685.39       $732.2731   $732.28   $732.25   $732.20