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 $184.61   8.173%   $199.6982   $199.70   $199.70   $199.70  
  Purchase #2 $212.53   3.171%   $219.2693   $219.27   $219.25   $219.30  
  Purchase #3 $243.31   8.301%   $263.5072   $263.51   $263.50   $263.50  
  Purchase #4 $61.40   11.711%   $68.5906   $68.59   $68.60   $68.60  
  Purchase #5 $24.90   12.348%   $27.9747   $27.97   $27.95   $28.00  
  Purchase #6 $245.36   6.746%   $261.912   $261.91   $261.90   $261.90  
  Purchase #7 $177.77   11.121%   $197.5398   $197.54   $197.55   $197.50  
  7 purchase totals = $1,149.88       $1,238.4918   $1,238.49   $1,238.45   $1,238.50