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 $152.75   8.771%   $166.1477   $166.15   $166.15   $166.10  
  Purchase #2 $241.91   10.466%   $267.2283   $267.23   $267.25   $267.20  
  Purchase #3 $64.44   6.283%   $68.4888   $68.49   $68.50   $68.50  
  Purchase #4 $106.50   6.714%   $113.6504   $113.65   $113.65   $113.70  
  Purchase #5 $140.78   12.228%   $157.9946   $157.99   $158.00   $158.00  
  Purchase #6 $157.91   10.312%   $174.1937   $174.19   $174.20   $174.20  
  Purchase #7 $93.43   8.323%   $101.2062   $101.21   $101.20   $101.20  
  7 purchase totals = $957.72       $1,048.9097   $1,048.91   $1,048.95   $1,048.90