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 $229.87   11.319%   $255.889   $255.89   $255.90   $255.90  
  Purchase #2 $128.71   4.614%   $134.6487   $134.65   $134.65   $134.60  
  Purchase #3 $8.48   8.631%   $9.2119   $9.21   $9.20   $9.20  
  Purchase #4 $48.48   12.623%   $54.5996   $54.60   $54.60   $54.60  
  Purchase #5 $221.59   4.860%   $232.3593   $232.36   $232.35   $232.40  
  Purchase #6 $158.48   4.211%   $165.1536   $165.15   $165.15   $165.20  
  Purchase #7 $158.85   13.236%   $179.8754   $179.88   $179.90   $179.90  
  7 purchase totals = $954.46       $1,031.7375   $1,031.74   $1,031.75   $1,031.80