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 $203.62   12.812%   $229.7078   $229.71   $229.70   $229.70  
  Purchase #2 $36.87   6.125%   $39.1283   $39.13   $39.15   $39.10  
  Purchase #3 $74.59   11.153%   $82.909   $82.91   $82.90   $82.90  
  Purchase #4 $98.94   9.713%   $108.55   $108.55   $108.55   $108.60  
  Purchase #5 $75.73   6.469%   $80.629   $80.63   $80.65   $80.60  
  Purchase #6 $234.74   7.714%   $252.8478   $252.85   $252.85   $252.80  
  Purchase #7 $158.45   4.137%   $165.0051   $165.01   $165.00   $165.00  
  7 purchase totals = $882.94       $958.7770   $958.79   $958.80   $958.70