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 $88.87   11.160%   $98.7879   $98.79   $98.80   $98.80  
  Purchase #2 $189.55   7.314%   $203.4137   $203.41   $203.40   $203.40  
  Purchase #3 $190.65   11.699%   $212.9541   $212.95   $212.95   $213.00  
  Purchase #4 $52.85   11.324%   $58.8347   $58.83   $58.85   $58.80  
  Purchase #5 $209.61   11.461%   $233.6334   $233.63   $233.65   $233.60  
  Purchase #6 $246.54   5.740%   $260.6914   $260.69   $260.70   $260.70  
  Purchase #7 $43.45   11.310%   $48.3642   $48.36   $48.35   $48.40  
  7 purchase totals = $1,021.52       $1,116.6794   $1,116.66   $1,116.70   $1,116.70