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 $107.38   7.111%   $115.0158   $115.02   $115.00   $115.00  
  Purchase #2 $145.73   4.473%   $152.2485   $152.25   $152.25   $152.20  
  Purchase #3 $163.64   12.449%   $184.0115   $184.01   $184.00   $184.00  
  Purchase #4 $52.31   7.358%   $56.159   $56.16   $56.15   $56.20  
  Purchase #5 $200.46   12.729%   $225.9766   $225.98   $226.00   $226.00  
  Purchase #6 $61.54   7.340%   $66.057   $66.06   $66.05   $66.10  
  Purchase #7 $247.72   7.786%   $267.0075   $267.01   $267.00   $267.00  
  7 purchase totals = $978.78       $1,066.4759   $1,066.49   $1,066.45   $1,066.50