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 $245.35   6.251%   $260.6868   $260.69   $260.70   $260.70  
  Purchase #2 $161.64   11.204%   $179.7501   $179.75   $179.75   $179.80  
  Purchase #3 $215.98   8.188%   $233.6644   $233.66   $233.65   $233.70  
  Purchase #4 $32.62   3.249%   $33.6798   $33.68   $33.70   $33.70  
  Purchase #5 $74.95   12.785%   $84.5324   $84.53   $84.55   $84.50  
  Purchase #6 $119.79   3.871%   $124.4271   $124.43   $124.45   $124.40  
  Purchase #7 $131.92   12.273%   $148.1105   $148.11   $148.10   $148.10  
  7 purchase totals = $982.25       $1,064.8511   $1,064.85   $1,064.90   $1,064.90