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 $91.69   11.273%   $102.0262   $102.03   $102.05   $102.00  
  Purchase #2 $218.76   5.127%   $229.9758   $229.98   $230.00   $230.00  
  Purchase #3 $49.80   13.544%   $56.5449   $56.54   $56.55   $56.50  
  Purchase #4 $56.73   9.765%   $62.2697   $62.27   $62.25   $62.30  
  Purchase #5 $24.28   13.497%   $27.5571   $27.56   $27.55   $27.60  
  Purchase #6 $93.50   13.689%   $106.2992   $106.30   $106.30   $106.30  
  Purchase #7 $164.75   13.222%   $186.5332   $186.53   $186.55   $186.50  
  7 purchase totals = $699.51       $771.2061   $771.21   $771.25   $771.20