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 $216.64   13.326%   $245.5094   $245.51   $245.50   $245.50  
  Purchase #2 $228.89   12.707%   $257.9751   $257.98   $258.00   $258.00  
  Purchase #3 $8.42   6.182%   $8.9405   $8.94   $8.95   $8.90  
  Purchase #4 $194.87   7.292%   $209.0799   $209.08   $209.10   $209.10  
  Purchase #5 $176.70   11.761%   $197.4817   $197.48   $197.50   $197.50  
  Purchase #6 $194.40   5.425%   $204.9462   $204.95   $204.95   $204.90  
  Purchase #7 $56.59   3.221%   $58.4128   $58.41   $58.40   $58.40  
  7 purchase totals = $1,076.51       $1,182.3456   $1,182.35   $1,182.40   $1,182.30