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 $66.98   6.802%   $71.536   $71.54   $71.55   $71.50  
  Purchase #2 $243.29   3.729%   $252.3623   $252.36   $252.35   $252.40  
  Purchase #3 $61.42   3.328%   $63.4641   $63.46   $63.45   $63.50  
  Purchase #4 $208.32   11.275%   $231.8081   $231.81   $231.80   $231.80  
  Purchase #5 $75.56   10.474%   $83.4742   $83.47   $83.45   $83.50  
  Purchase #6 $53.33   6.199%   $56.6359   $56.64   $56.65   $56.60  
  Purchase #7 $93.84   13.550%   $106.5553   $106.56   $106.55   $106.60  
  7 purchase totals = $802.74       $865.8359   $865.84   $865.80   $865.90