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 $64.34   5.318%   $67.7616   $67.76   $67.75   $67.80  
  Purchase #2 $77.68   6.654%   $82.8488   $82.85   $82.85   $82.80  
  Purchase #3 $97.69   10.463%   $107.9113   $107.91   $107.90   $107.90  
  Purchase #4 $120.69   5.693%   $127.5609   $127.56   $127.55   $127.60  
  Purchase #5 $111.93   5.439%   $118.0179   $118.02   $118.00   $118.00  
  Purchase #6 $20.34   8.357%   $22.0398   $22.04   $22.05   $22.00  
  Purchase #7 $193.58   6.510%   $206.1821   $206.18   $206.20   $206.20  
  7 purchase totals = $686.25       $732.3224   $732.32   $732.30   $732.30