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 $204.78   5.253%   $215.5371   $215.54   $215.55   $215.50  
  Purchase #2 $57.43   13.598%   $65.2393   $65.24   $65.25   $65.20  
  Purchase #3 $228.93   13.393%   $259.5906   $259.59   $259.60   $259.60  
  Purchase #4 $165.26   9.186%   $180.4408   $180.44   $180.45   $180.40  
  Purchase #5 $231.73   6.303%   $246.3359   $246.34   $246.35   $246.30  
  Purchase #6 $135.67   12.634%   $152.8105   $152.81   $152.80   $152.80  
  Purchase #7 $223.68   8.603%   $242.9232   $242.92   $242.90   $242.90  
  7 purchase totals = $1,247.48       $1,362.8774   $1,362.88   $1,362.90   $1,362.70