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 $29.88   13.623%   $33.9506   $33.95   $33.95   $34.00  
  Purchase #2 $243.37   5.117%   $255.8232   $255.82   $255.80   $255.80  
  Purchase #3 $159.70   9.527%   $174.9146   $174.91   $174.90   $174.90  
  Purchase #4 $217.26   8.143%   $234.9515   $234.95   $234.95   $235.00  
  Purchase #5 $15.49   7.738%   $16.6886   $16.69   $16.70   $16.70  
  Purchase #6 $113.25   10.146%   $124.7403   $124.74   $124.75   $124.70  
  Purchase #7 $220.81   5.360%   $232.6454   $232.65   $232.65   $232.60  
  7 purchase totals = $999.76       $1,073.7142   $1,073.71   $1,073.70   $1,073.70