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 $95.61   4.462%   $99.8761   $99.88   $99.90   $99.90  
  Purchase #2 $49.98   13.373%   $56.6638   $56.66   $56.65   $56.70  
  Purchase #3 $154.69   13.469%   $175.5252   $175.53   $175.55   $175.50  
  Purchase #4 $70.65   9.258%   $77.1908   $77.19   $77.20   $77.20  
  Purchase #5 $74.95   7.270%   $80.3989   $80.40   $80.40   $80.40  
  Purchase #6 $205.32   7.228%   $220.1605   $220.16   $220.15   $220.20  
  Purchase #7 $68.79   10.502%   $76.0143   $76.01   $76.00   $76.00  
  7 purchase totals = $719.99       $785.8296   $785.83   $785.85   $785.90