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 $58.89   11.436%   $65.6247   $65.62   $65.60   $65.60  
  Purchase #2 $171.47   6.689%   $182.9396   $182.94   $182.95   $182.90  
  Purchase #3 $165.51   13.437%   $187.7496   $187.75   $187.75   $187.70  
  Purchase #4 $53.63   6.189%   $56.9492   $56.95   $56.95   $56.90  
  Purchase #5 $122.38   10.325%   $135.0157   $135.02   $135.00   $135.00  
  Purchase #6 $148.63   4.714%   $155.6364   $155.64   $155.65   $155.60  
  Purchase #7 $82.73   8.394%   $89.6744   $89.67   $89.65   $89.70  
  7 purchase totals = $803.24       $873.5896   $873.59   $873.55   $873.40