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 $166.82   12.258%   $187.2688   $187.27   $187.25   $187.30  
  Purchase #2 $127.53   7.273%   $136.8053   $136.81   $136.80   $136.80  
  Purchase #3 $150.76   7.703%   $162.373   $162.37   $162.35   $162.40  
  Purchase #4 $220.50   10.185%   $242.9579   $242.96   $242.95   $243.00  
  Purchase #5 $205.55   4.854%   $215.5274   $215.53   $215.55   $215.50  
  Purchase #6 $42.95   10.841%   $47.6062   $47.61   $47.60   $47.60  
  Purchase #7 $20.62   12.257%   $23.1474   $23.15   $23.15   $23.10  
  7 purchase totals = $934.73       $1,015.6860   $1,015.70   $1,015.65   $1,015.70