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 $147.58   12.176%   $165.5493   $165.55   $165.55   $165.50  
  Purchase #2 $47.45   7.607%   $51.0595   $51.06   $51.05   $51.10  
  Purchase #3 $110.96   6.812%   $118.5186   $118.52   $118.50   $118.50  
  Purchase #4 $239.33   8.252%   $259.0795   $259.08   $259.10   $259.10  
  Purchase #5 $198.72   9.590%   $217.7772   $217.78   $217.80   $217.80  
  Purchase #6 $118.25   7.348%   $126.939   $126.94   $126.95   $126.90  
  Purchase #7 $132.42   5.721%   $139.9957   $140.00   $140.00   $140.00  
  7 purchase totals = $994.71       $1,078.9188   $1,078.93   $1,078.95   $1,078.90