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 $240.43   11.119%   $267.1634   $267.16   $267.15   $267.20  
  Purchase #2 $157.28   11.695%   $175.6739   $175.67   $175.65   $175.70  
  Purchase #3 $206.90   12.103%   $231.9411   $231.94   $231.95   $231.90  
  Purchase #4 $54.41   6.611%   $58.007   $58.01   $58.00   $58.00  
  Purchase #5 $222.62   8.261%   $241.0106   $241.01   $241.00   $241.00  
  Purchase #6 $190.95   6.371%   $203.1154   $203.12   $203.10   $203.10  
  Purchase #7 $21.49   11.624%   $23.988   $23.99   $24.00   $24.00  
  7 purchase totals = $1,094.08       $1,200.8994   $1,200.90   $1,200.85   $1,200.90