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 $118.64   5.401%   $125.0477   $125.05   $125.05   $125.00  
  Purchase #2 $45.83   13.765%   $52.1385   $52.14   $52.15   $52.10  
  Purchase #3 $242.55   12.115%   $271.9349   $271.93   $271.95   $271.90  
  Purchase #4 $52.31   8.446%   $56.7281   $56.73   $56.75   $56.70  
  Purchase #5 $212.95   4.687%   $222.931   $222.93   $222.95   $222.90  
  Purchase #6 $38.66   6.451%   $41.154   $41.15   $41.15   $41.20  
  Purchase #7 $17.85   4.351%   $18.6267   $18.63   $18.65   $18.60  
  7 purchase totals = $728.79       $788.5609   $788.56   $788.65   $788.40