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 $167.97   6.163%   $178.322   $178.32   $178.30   $178.30  
  Purchase #2 $87.90   11.662%   $98.1509   $98.15   $98.15   $98.20  
  Purchase #3 $24.96   8.418%   $27.0611   $27.06   $27.05   $27.10  
  Purchase #4 $243.76   8.767%   $265.1304   $265.13   $265.15   $265.10  
  Purchase #5 $43.34   7.367%   $46.5329   $46.53   $46.55   $46.50  
  Purchase #6 $144.80   7.395%   $155.508   $155.51   $155.50   $155.50  
  Purchase #7 $225.62   11.818%   $252.2838   $252.28   $252.30   $252.30  
  7 purchase totals = $938.35       $1,022.9891   $1,022.98   $1,023.00   $1,023.00