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 $246.85   11.340%   $274.8428   $274.84   $274.85   $274.80  
  Purchase #2 $149.55   3.135%   $154.2384   $154.24   $154.25   $154.20  
  Purchase #3 $156.90   13.627%   $178.2808   $178.28   $178.30   $178.30  
  Purchase #4 $57.29   13.543%   $65.0488   $65.05   $65.05   $65.00  
  Purchase #5 $242.97   3.114%   $250.5361   $250.54   $250.55   $250.50  
  Purchase #6 $42.92   8.320%   $46.4909   $46.49   $46.50   $46.50  
  Purchase #7 $206.33   13.644%   $234.4817   $234.48   $234.50   $234.50  
  7 purchase totals = $1,102.81       $1,203.9195   $1,203.92   $1,204.00   $1,203.80