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 $62.35   5.523%   $65.7936   $65.79   $65.80   $65.80  
  Purchase #2 $9.66   6.106%   $10.2498   $10.25   $10.25   $10.20  
  Purchase #3 $108.48   11.232%   $120.6645   $120.66   $120.65   $120.70  
  Purchase #4 $119.47   12.106%   $133.933   $133.93   $133.95   $133.90  
  Purchase #5 $226.93   8.845%   $247.002   $247.00   $247.00   $247.00  
  Purchase #6 $97.95   4.525%   $102.3822   $102.38   $102.40   $102.40  
  Purchase #7 $210.86   6.731%   $225.053   $225.05   $225.05   $225.10  
  7 purchase totals = $835.70       $905.0781   $905.06   $905.10   $905.10