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 $206.95   9.216%   $226.0225   $226.02   $226.00   $226.00  
  Purchase #2 $158.56   11.808%   $177.2828   $177.28   $177.30   $177.30  
  Purchase #3 $51.65   5.431%   $54.4551   $54.46   $54.45   $54.50  
  Purchase #4 $55.25   5.596%   $58.3418   $58.34   $58.35   $58.30  
  Purchase #5 $164.46   10.296%   $181.3928   $181.39   $181.40   $181.40  
  Purchase #6 $178.46   5.246%   $187.822   $187.82   $187.80   $187.80  
  Purchase #7 $201.67   5.523%   $212.8082   $212.81   $212.80   $212.80  
  7 purchase totals = $1,017.00       $1,098.1252   $1,098.12   $1,098.10   $1,098.10