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 $68.55   11.814%   $76.6485   $76.65   $76.65   $76.60  
  Purchase #2 $250.27   5.606%   $264.3001   $264.30   $264.30   $264.30  
  Purchase #3 $200.59   6.134%   $212.8942   $212.89   $212.90   $212.90  
  Purchase #4 $228.35   13.874%   $260.0313   $260.03   $260.05   $260.00  
  Purchase #5 $64.32   9.463%   $70.4066   $70.41   $70.40   $70.40  
  Purchase #6 $148.61   6.463%   $158.2147   $158.21   $158.20   $158.20  
  Purchase #7 $175.57   5.662%   $185.5108   $185.51   $185.50   $185.50  
  7 purchase totals = $1,136.26       $1,228.0062   $1,228.00   $1,228.00   $1,227.90