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 $76.28   12.490%   $85.8074   $85.81   $85.80   $85.80  
  Purchase #2 $165.65   5.617%   $174.9546   $174.95   $174.95   $175.00  
  Purchase #3 $24.93   6.287%   $26.4973   $26.50   $26.50   $26.50  
  Purchase #4 $162.70   3.780%   $168.8501   $168.85   $168.85   $168.90  
  Purchase #5 $123.88   6.169%   $131.5222   $131.52   $131.50   $131.50  
  Purchase #6 $24.86   12.268%   $27.9098   $27.91   $27.90   $27.90  
  Purchase #7 $121.48   13.755%   $138.1896   $138.19   $138.20   $138.20  
  7 purchase totals = $699.78       $753.7310   $753.73   $753.70   $753.80