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 $240.94   10.320%   $265.805   $265.81   $265.80   $265.80  
  Purchase #2 $174.72   10.824%   $193.6317   $193.63   $193.65   $193.60  
  Purchase #3 $20.61   8.384%   $22.3379   $22.34   $22.35   $22.30  
  Purchase #4 $61.86   5.331%   $65.1578   $65.16   $65.15   $65.20  
  Purchase #5 $137.86   12.678%   $155.3379   $155.34   $155.35   $155.30  
  Purchase #6 $245.31   11.710%   $274.0358   $274.04   $274.05   $274.00  
  Purchase #7 $81.77   12.309%   $91.8351   $91.84   $91.85   $91.80  
  7 purchase totals = $963.07       $1,068.1412   $1,068.16   $1,068.20   $1,068.00