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 $211.50   11.217%   $235.224   $235.22   $235.20   $235.20  
  Purchase #2 $34.50   11.674%   $38.5275   $38.53   $38.55   $38.50  
  Purchase #3 $183.52   11.660%   $204.9184   $204.92   $204.90   $204.90  
  Purchase #4 $98.62   9.348%   $107.839   $107.84   $107.85   $107.80  
  Purchase #5 $234.28   9.836%   $257.3238   $257.32   $257.30   $257.30  
  Purchase #6 $72.56   5.296%   $76.4028   $76.40   $76.40   $76.40  
  Purchase #7 $190.71   11.307%   $212.2736   $212.27   $212.25   $212.30  
  7 purchase totals = $1,025.69       $1,132.5091   $1,132.50   $1,132.45   $1,132.40