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 $75.95   13.204%   $85.9784   $85.98   $86.00   $86.00  
  Purchase #2 $100.63   6.199%   $106.8681   $106.87   $106.85   $106.90  
  Purchase #3 $114.76   11.368%   $127.8059   $127.81   $127.80   $127.80  
  Purchase #4 $187.80   8.208%   $203.2146   $203.21   $203.20   $203.20  
  Purchase #5 $21.95   7.772%   $23.656   $23.66   $23.65   $23.70  
  Purchase #6 $28.36   8.310%   $30.7167   $30.72   $30.70   $30.70  
  Purchase #7 $249.32   10.732%   $276.077   $276.08   $276.10   $276.10  
  7 purchase totals = $778.77       $854.3167   $854.33   $854.30   $854.40