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 $110.83   5.661%   $117.1041   $117.10   $117.10   $117.10  
  Purchase #2 $214.45   11.153%   $238.3676   $238.37   $238.35   $238.40  
  Purchase #3 $90.30   13.593%   $102.5745   $102.57   $102.55   $102.60  
  Purchase #4 $246.72   12.573%   $277.7401   $277.74   $277.75   $277.70  
  Purchase #5 $58.70   7.468%   $63.0837   $63.08   $63.10   $63.10  
  Purchase #6 $142.28   7.145%   $152.4459   $152.45   $152.45   $152.40  
  Purchase #7 $41.92   11.377%   $46.6892   $46.69   $46.70   $46.70  
  7 purchase totals = $905.20       $998.0051   $998.00   $998.00   $998.00