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 $61.59   10.737%   $68.2029   $68.20   $68.20   $68.20  
  Purchase #2 $132.62   7.115%   $142.0559   $142.06   $142.05   $142.10  
  Purchase #3 $163.62   12.461%   $184.0087   $184.01   $184.00   $184.00  
  Purchase #4 $48.31   8.138%   $52.2415   $52.24   $52.25   $52.20  
  Purchase #5 $54.72   12.783%   $61.7149   $61.71   $61.70   $61.70  
  Purchase #6 $94.78   12.302%   $106.4398   $106.44   $106.45   $106.40  
  Purchase #7 $186.63   13.480%   $211.7877   $211.79   $211.80   $211.80  
  7 purchase totals = $742.27       $826.4514   $826.45   $826.45   $826.40