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 $76.92   7.537%   $82.7175   $82.72   $82.70   $82.70  
  Purchase #2 $223.95   13.395%   $253.9481   $253.95   $253.95   $253.90  
  Purchase #3 $50.70   9.403%   $55.4673   $55.47   $55.45   $55.50  
  Purchase #4 $172.97   7.795%   $186.453   $186.45   $186.45   $186.50  
  Purchase #5 $5.89   3.868%   $6.1178   $6.12   $6.10   $6.10  
  Purchase #6 $95.25   7.270%   $102.1747   $102.17   $102.15   $102.20  
  Purchase #7 $80.86   9.471%   $88.5183   $88.52   $88.50   $88.50  
  7 purchase totals = $706.54       $775.3967   $775.40   $775.30   $775.40