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 $61.34   4.136%   $63.877   $63.88   $63.90   $63.90  
  Purchase #2 $85.43   10.409%   $94.3224   $94.32   $94.30   $94.30  
  Purchase #3 $55.65   5.688%   $58.8154   $58.82   $58.80   $58.80  
  Purchase #4 $43.30   10.767%   $47.9621   $47.96   $47.95   $48.00  
  Purchase #5 $242.49   6.586%   $258.4604   $258.46   $258.45   $258.50  
  Purchase #6 $124.52   8.582%   $135.2063   $135.21   $135.20   $135.20  
  Purchase #7 $114.88   10.702%   $127.1745   $127.17   $127.15   $127.20  
  7 purchase totals = $727.61       $785.8181   $785.82   $785.75   $785.90