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 $246.33   6.869%   $263.2504   $263.25   $263.25   $263.30  
  Purchase #2 $98.57   11.830%   $110.2308   $110.23   $110.25   $110.20  
  Purchase #3 $5.53   13.560%   $6.2799   $6.28   $6.30   $6.30  
  Purchase #4 $180.88   13.795%   $205.8324   $205.83   $205.85   $205.80  
  Purchase #5 $23.51   5.726%   $24.8562   $24.86   $24.85   $24.90  
  Purchase #6 $238.98   4.630%   $250.0448   $250.04   $250.05   $250.00  
  Purchase #7 $247.97   8.782%   $269.7467   $269.75   $269.75   $269.70  
  7 purchase totals = $1,041.77       $1,130.2412   $1,130.24   $1,130.30   $1,130.20