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 $145.74   6.650%   $155.4317   $155.43   $155.45   $155.40  
  Purchase #2 $212.97   12.530%   $239.6551   $239.66   $239.65   $239.70  
  Purchase #3 $235.54   5.748%   $249.0788   $249.08   $249.10   $249.10  
  Purchase #4 $106.64   4.372%   $111.3023   $111.30   $111.30   $111.30  
  Purchase #5 $203.90   4.393%   $212.8573   $212.86   $212.85   $212.90  
  Purchase #6 $69.26   8.678%   $75.2704   $75.27   $75.25   $75.30  
  Purchase #7 $51.28   4.380%   $53.5261   $53.53   $53.55   $53.50  
  7 purchase totals = $1,025.33       $1,097.1217   $1,097.13   $1,097.15   $1,097.20