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 $165.49   11.631%   $184.7381   $184.74   $184.75   $184.70  
  Purchase #2 $38.76   11.714%   $43.3003   $43.30   $43.30   $43.30  
  Purchase #3 $102.65   12.547%   $115.5295   $115.53   $115.55   $115.50  
  Purchase #4 $245.45   3.598%   $254.2813   $254.28   $254.30   $254.30  
  Purchase #5 $31.53   8.725%   $34.281   $34.28   $34.30   $34.30  
  Purchase #6 $199.93   5.517%   $210.9601   $210.96   $210.95   $211.00  
  Purchase #7 $160.91   3.652%   $166.7864   $166.79   $166.80   $166.80  
  7 purchase totals = $944.72       $1,009.8767   $1,009.88   $1,009.95   $1,009.90