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 $182.32   10.541%   $201.5384   $201.54   $201.55   $201.50  
  Purchase #2 $115.59   13.417%   $131.0987   $131.10   $131.10   $131.10  
  Purchase #3 $110.66   7.206%   $118.6342   $118.63   $118.65   $118.60  
  Purchase #4 $229.84   10.212%   $253.3113   $253.31   $253.30   $253.30  
  Purchase #5 $54.55   11.830%   $61.0033   $61.00   $61.00   $61.00  
  Purchase #6 $178.44   6.697%   $190.3901   $190.39   $190.40   $190.40  
  Purchase #7 $87.25   12.693%   $98.3246   $98.32   $98.30   $98.30  
  7 purchase totals = $958.65       $1,054.3006   $1,054.29   $1,054.30   $1,054.20