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 $50.94   7.483%   $54.7518   $54.75   $54.75   $54.80  
  Purchase #2 $131.69   6.424%   $140.1498   $140.15   $140.15   $140.10  
  Purchase #3 $176.47   12.711%   $198.9011   $198.90   $198.90   $198.90  
  Purchase #4 $71.91   3.626%   $74.5175   $74.52   $74.50   $74.50  
  Purchase #5 $250.93   12.494%   $282.2812   $282.28   $282.30   $282.30  
  Purchase #6 $196.70   8.755%   $213.9211   $213.92   $213.90   $213.90  
  Purchase #7 $54.99   7.541%   $59.1368   $59.14   $59.15   $59.10  
  7 purchase totals = $933.63       $1,023.6593   $1,023.66   $1,023.65   $1,023.60