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 $80.49   4.283%   $83.9374   $83.94   $83.95   $83.90  
  Purchase #2 $61.92   8.127%   $66.9522   $66.95   $66.95   $67.00  
  Purchase #3 $219.64   3.361%   $227.0221   $227.02   $227.00   $227.00  
  Purchase #4 $179.45   11.221%   $199.5861   $199.59   $199.60   $199.60  
  Purchase #5 $161.51   9.509%   $176.868   $176.87   $176.85   $176.90  
  Purchase #6 $23.70   4.570%   $24.7831   $24.78   $24.80   $24.80  
  Purchase #7 $72.92   12.742%   $82.2115   $82.21   $82.20   $82.20  
  7 purchase totals = $799.63       $861.3604   $861.36   $861.35   $861.40