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 $83.93   13.255%   $95.0549   $95.05   $95.05   $95.10  
  Purchase #2 $218.81   10.805%   $242.4524   $242.45   $242.45   $242.50  
  Purchase #3 $129.39   7.433%   $139.0076   $139.01   $139.00   $139.00  
  Purchase #4 $61.95   7.560%   $66.6334   $66.63   $66.65   $66.60  
  Purchase #5 $24.78   12.502%   $27.878   $27.88   $27.90   $27.90  
  Purchase #6 $179.70   12.232%   $201.6809   $201.68   $201.70   $201.70  
  Purchase #7 $70.53   3.102%   $72.7178   $72.72   $72.70   $72.70  
  7 purchase totals = $769.09       $845.4250   $845.42   $845.45   $845.50