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 $40.85   5.447%   $43.0751   $43.08   $43.10   $43.10  
  Purchase #2 $215.41   7.643%   $231.8738   $231.87   $231.85   $231.90  
  Purchase #3 $192.80   11.483%   $214.9392   $214.94   $214.95   $214.90  
  Purchase #4 $159.61   11.185%   $177.4624   $177.46   $177.45   $177.50  
  Purchase #5 $55.99   7.806%   $60.3606   $60.36   $60.35   $60.40  
  Purchase #6 $72.93   13.787%   $82.9849   $82.98   $83.00   $83.00  
  Purchase #7 $187.39   13.475%   $212.6408   $212.64   $212.65   $212.60  
  7 purchase totals = $924.98       $1,023.3368   $1,023.33   $1,023.35   $1,023.40