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 $92.59   9.629%   $101.5055   $101.51   $101.50   $101.50  
  Purchase #2 $177.33   6.377%   $188.6383   $188.64   $188.65   $188.60  
  Purchase #3 $73.50   5.779%   $77.7476   $77.75   $77.75   $77.70  
  Purchase #4 $160.53   10.443%   $177.2941   $177.29   $177.30   $177.30  
  Purchase #5 $127.42   6.613%   $135.8463   $135.85   $135.85   $135.80  
  Purchase #6 $135.58   12.584%   $152.6414   $152.64   $152.65   $152.60  
  Purchase #7 $152.66   9.504%   $167.1688   $167.17   $167.15   $167.20  
  7 purchase totals = $919.61       $1,000.8420   $1,000.85   $1,000.85   $1,000.70