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 $61.82   6.762%   $66.0003   $66.00   $66.00   $66.00  
  Purchase #2 $168.84   11.474%   $188.2127   $188.21   $188.20   $188.20  
  Purchase #3 $58.92   10.549%   $65.1355   $65.14   $65.15   $65.10  
  Purchase #4 $174.85   10.261%   $192.7914   $192.79   $192.80   $192.80  
  Purchase #5 $238.37   13.119%   $269.6418   $269.64   $269.65   $269.60  
  Purchase #6 $63.25   9.168%   $69.0488   $69.05   $69.05   $69.00  
  Purchase #7 $105.29   5.129%   $110.6903   $110.69   $110.70   $110.70  
  7 purchase totals = $871.34       $961.5208   $961.52   $961.55   $961.40