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 $61.95   10.632%   $68.5365   $68.54   $68.55   $68.50  
  Purchase #2 $17.83   11.134%   $19.8152   $19.82   $19.80   $19.80  
  Purchase #3 $184.36   10.673%   $204.0367   $204.04   $204.05   $204.00  
  Purchase #4 $88.37   6.184%   $93.8348   $93.83   $93.85   $93.80  
  Purchase #5 $64.40   10.779%   $71.3417   $71.34   $71.35   $71.30  
  Purchase #6 $240.65   11.795%   $269.0347   $269.03   $269.05   $269.00  
  Purchase #7 $65.65   10.541%   $72.5702   $72.57   $72.55   $72.60  
  7 purchase totals = $723.21       $799.1698   $799.17   $799.20   $799.00