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 $56.35   8.772%   $61.293   $61.29   $61.30   $61.30  
  Purchase #2 $224.52   9.568%   $246.0021   $246.00   $246.00   $246.00  
  Purchase #3 $105.73   8.191%   $114.3903   $114.39   $114.40   $114.40  
  Purchase #4 $197.41   10.801%   $218.7323   $218.73   $218.75   $218.70  
  Purchase #5 $71.83   12.105%   $80.525   $80.53   $80.55   $80.50  
  Purchase #6 $22.35   8.685%   $24.2911   $24.29   $24.30   $24.30  
  Purchase #7 $232.89   4.191%   $242.6504   $242.65   $242.65   $242.70  
  7 purchase totals = $911.08       $987.8842   $987.88   $987.95   $987.90