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 $240.62   10.465%   $265.8009   $265.80   $265.80   $265.80  
  Purchase #2 $150.33   8.652%   $163.3366   $163.34   $163.35   $163.30  
  Purchase #3 $79.43   5.736%   $83.9861   $83.99   $84.00   $84.00  
  Purchase #4 $112.29   12.869%   $126.7406   $126.74   $126.75   $126.70  
  Purchase #5 $96.34   10.402%   $106.3613   $106.36   $106.35   $106.40  
  Purchase #6 $246.81   10.136%   $271.8267   $271.83   $271.85   $271.80  
  Purchase #7 $55.27   6.589%   $58.9117   $58.91   $58.90   $58.90  
  7 purchase totals = $981.09       $1,076.9639   $1,076.97   $1,077.00   $1,076.90