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 $160.93   8.320%   $174.3194   $174.32   $174.30   $174.30  
  Purchase #2 $173.46   12.224%   $194.6638   $194.66   $194.65   $194.70  
  Purchase #3 $139.76   8.815%   $152.0798   $152.08   $152.10   $152.10  
  Purchase #4 $53.29   13.493%   $60.4804   $60.48   $60.50   $60.50  
  Purchase #5 $63.86   9.322%   $69.813   $69.81   $69.80   $69.80  
  Purchase #6 $42.55   12.401%   $47.8266   $47.83   $47.85   $47.80  
  Purchase #7 $210.67   6.798%   $224.9913   $224.99   $225.00   $225.00  
  7 purchase totals = $844.52       $924.1743   $924.17   $924.20   $924.20