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 $152.42   9.144%   $166.3573   $166.36   $166.35   $166.40  
  Purchase #2 $119.66   8.306%   $129.599   $129.60   $129.60   $129.60  
  Purchase #3 $18.84   5.108%   $19.8023   $19.80   $19.80   $19.80  
  Purchase #4 $207.85   9.437%   $227.4648   $227.46   $227.45   $227.50  
  Purchase #5 $77.80   6.358%   $82.7465   $82.75   $82.75   $82.70  
  Purchase #6 $219.96   6.842%   $235.0097   $235.01   $235.00   $235.00  
  Purchase #7 $151.49   7.764%   $163.2517   $163.25   $163.25   $163.30  
  7 purchase totals = $948.02       $1,024.2313   $1,024.23   $1,024.20   $1,024.30