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 $220.52   9.584%   $241.6546   $241.65   $241.65   $241.70  
  Purchase #2 $247.55   5.671%   $261.5886   $261.59   $261.60   $261.60  
  Purchase #3 $50.76   6.289%   $53.9523   $53.95   $53.95   $54.00  
  Purchase #4 $250.69   6.627%   $267.3032   $267.30   $267.30   $267.30  
  Purchase #5 $24.80   6.191%   $26.3354   $26.34   $26.35   $26.30  
  Purchase #6 $145.65   3.106%   $150.1739   $150.17   $150.15   $150.20  
  Purchase #7 $176.71   11.844%   $197.6395   $197.64   $197.65   $197.60  
  7 purchase totals = $1,116.68       $1,198.6475   $1,198.64   $1,198.65   $1,198.70