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 $123.75   9.862%   $135.9542   $135.95   $135.95   $136.00  
  Purchase #2 $37.60   9.138%   $41.0359   $41.04   $41.05   $41.00  
  Purchase #3 $217.48   3.617%   $225.3463   $225.35   $225.35   $225.30  
  Purchase #4 $93.36   11.702%   $104.285   $104.29   $104.30   $104.30  
  Purchase #5 $226.56   8.871%   $246.6581   $246.66   $246.65   $246.70  
  Purchase #6 $60.35   9.589%   $66.137   $66.14   $66.15   $66.10  
  Purchase #7 $165.45   5.531%   $174.601   $174.60   $174.60   $174.60  
  7 purchase totals = $924.55       $994.0175   $994.03   $994.05   $994.00