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 $31.60   10.286%   $34.8504   $34.85   $34.85   $34.90  
  Purchase #2 $201.59   5.329%   $212.3327   $212.33   $212.35   $212.30  
  Purchase #3 $163.89   4.368%   $171.0487   $171.05   $171.05   $171.00  
  Purchase #4 $238.90   11.610%   $266.6363   $266.64   $266.65   $266.60  
  Purchase #5 $98.62   3.305%   $101.8794   $101.88   $101.90   $101.90  
  Purchase #6 $146.29   13.348%   $165.8168   $165.82   $165.80   $165.80  
  Purchase #7 $101.99   13.716%   $115.9789   $115.98   $116.00   $116.00  
  7 purchase totals = $982.88       $1,068.5432   $1,068.55   $1,068.60   $1,068.50