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 $61.48   12.594%   $69.2228   $69.22   $69.20   $69.20  
  Purchase #2 $198.49   9.789%   $217.9202   $217.92   $217.90   $217.90  
  Purchase #3 $144.87   3.713%   $150.249   $150.25   $150.25   $150.20  
  Purchase #4 $23.92   5.658%   $25.2734   $25.27   $25.25   $25.30  
  Purchase #5 $161.31   8.456%   $174.9504   $174.95   $174.95   $175.00  
  Purchase #6 $247.27   4.604%   $258.6543   $258.65   $258.65   $258.70  
  Purchase #7 $28.85   5.141%   $30.3332   $30.33   $30.35   $30.30  
  7 purchase totals = $866.19       $926.6033   $926.59   $926.55   $926.60