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 $63.49   4.154%   $66.1274   $66.13   $66.15   $66.10  
  Purchase #2 $133.33   13.452%   $151.2656   $151.27   $151.25   $151.30  
  Purchase #3 $98.93   8.371%   $107.2114   $107.21   $107.20   $107.20  
  Purchase #4 $239.97   12.107%   $269.0232   $269.02   $269.00   $269.00  
  Purchase #5 $32.84   6.723%   $35.0478   $35.05   $35.05   $35.00  
  Purchase #6 $120.81   4.717%   $126.5086   $126.51   $126.50   $126.50  
  Purchase #7 $165.65   9.576%   $181.5126   $181.51   $181.50   $181.50  
  7 purchase totals = $855.02       $936.6966   $936.70   $936.65   $936.60