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 $122.73   12.643%   $138.2468   $138.25   $138.25   $138.20  
  Purchase #2 $227.67   9.216%   $248.6521   $248.65   $248.65   $248.70  
  Purchase #3 $159.25   4.595%   $166.5675   $166.57   $166.55   $166.60  
  Purchase #4 $55.33   11.202%   $61.5281   $61.53   $61.55   $61.50  
  Purchase #5 $54.58   9.422%   $59.7225   $59.72   $59.70   $59.70  
  Purchase #6 $199.62   6.682%   $212.9586   $212.96   $212.95   $213.00  
  Purchase #7 $159.80   9.216%   $174.5272   $174.53   $174.55   $174.50  
  7 purchase totals = $978.98       $1,062.2028   $1,062.21   $1,062.20   $1,062.20