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 $46.92   5.493%   $49.4973   $49.50   $49.50   $49.50  
  Purchase #2 $96.91   7.236%   $103.9224   $103.92   $103.90   $103.90  
  Purchase #3 $156.99   11.648%   $175.2762   $175.28   $175.30   $175.30  
  Purchase #4 $97.78   11.852%   $109.3689   $109.37   $109.35   $109.40  
  Purchase #5 $244.53   8.439%   $265.1659   $265.17   $265.15   $265.20  
  Purchase #6 $125.56   5.198%   $132.0866   $132.09   $132.10   $132.10  
  Purchase #7 $152.94   8.406%   $165.7961   $165.80   $165.80   $165.80  
  7 purchase totals = $921.63       $1,001.1134   $1,001.13   $1,001.10   $1,001.20