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 $106.99   8.236%   $115.8017   $115.80   $115.80   $115.80  
  Purchase #2 $225.76   10.837%   $250.2256   $250.23   $250.25   $250.20  
  Purchase #3 $178.65   12.660%   $201.2671   $201.27   $201.25   $201.30  
  Purchase #4 $206.79   8.281%   $223.9143   $223.91   $223.90   $223.90  
  Purchase #5 $30.96   6.627%   $33.0117   $33.01   $33.00   $33.00  
  Purchase #6 $49.27   3.146%   $50.82   $50.82   $50.80   $50.80  
  Purchase #7 $234.69   11.733%   $262.2262   $262.23   $262.25   $262.20  
  7 purchase totals = $1,033.11       $1,137.2666   $1,137.27   $1,137.25   $1,137.20