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 $33.57   6.573%   $35.7766   $35.78   $35.80   $35.80  
  Purchase #2 $82.98   11.633%   $92.6331   $92.63   $92.65   $92.60  
  Purchase #3 $101.46   11.431%   $113.0579   $113.06   $113.05   $113.10  
  Purchase #4 $242.58   10.837%   $268.8684   $268.87   $268.85   $268.90  
  Purchase #5 $154.86   10.608%   $171.2875   $171.29   $171.30   $171.30  
  Purchase #6 $193.50   4.248%   $201.7199   $201.72   $201.70   $201.70  
  Purchase #7 $57.55   13.174%   $65.1316   $65.13   $65.15   $65.10  
  7 purchase totals = $866.50       $948.4750   $948.48   $948.50   $948.50