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 $52.87   9.629%   $57.9609   $57.96   $57.95   $58.00  
  Purchase #2 $172.59   5.345%   $181.8149   $181.81   $181.80   $181.80  
  Purchase #3 $75.52   7.543%   $81.2165   $81.22   $81.20   $81.20  
  Purchase #4 $229.98   8.252%   $248.9579   $248.96   $248.95   $249.00  
  Purchase #5 $6.97   4.732%   $7.2998   $7.30   $7.30   $7.30  
  Purchase #6 $188.96   10.404%   $208.6194   $208.62   $208.60   $208.60  
  Purchase #7 $232.43   8.127%   $251.3196   $251.32   $251.30   $251.30  
  7 purchase totals = $959.32       $1,037.1890   $1,037.19   $1,037.10   $1,037.20