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 $86.92   12.773%   $98.0223   $98.02   $98.00   $98.00  
  Purchase #2 $151.32   7.705%   $162.9792   $162.98   $163.00   $163.00  
  Purchase #3 $17.77   8.265%   $19.2387   $19.24   $19.25   $19.20  
  Purchase #4 $173.49   9.107%   $189.2897   $189.29   $189.30   $189.30  
  Purchase #5 $210.67   3.722%   $218.5111   $218.51   $218.50   $218.50  
  Purchase #6 $25.66   5.543%   $27.0823   $27.08   $27.10   $27.10  
  Purchase #7 $212.61   7.225%   $227.9711   $227.97   $227.95   $228.00  
  7 purchase totals = $878.44       $943.0944   $943.09   $943.10   $943.10