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 $58.85   5.297%   $61.9673   $61.97   $61.95   $62.00  
  Purchase #2 $172.97   7.253%   $185.5155   $185.52   $185.50   $185.50  
  Purchase #3 $74.33   13.747%   $84.5481   $84.55   $84.55   $84.50  
  Purchase #4 $200.62   9.366%   $219.4101   $219.41   $219.40   $219.40  
  Purchase #5 $5.42   12.822%   $6.115   $6.12   $6.10   $6.10  
  Purchase #6 $26.59   6.188%   $28.2354   $28.24   $28.25   $28.20  
  Purchase #7 $88.65   7.102%   $94.9459   $94.95   $94.95   $94.90  
  7 purchase totals = $627.43       $680.7373   $680.76   $680.70   $680.60