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 $54.57   13.217%   $61.7825   $61.78   $61.80   $61.80  
  Purchase #2 $243.31   12.763%   $274.3637   $274.36   $274.35   $274.40  
  Purchase #3 $227.67   11.513%   $253.8816   $253.88   $253.90   $253.90  
  Purchase #4 $173.33   3.401%   $179.225   $179.23   $179.25   $179.20  
  Purchase #5 $173.99   11.220%   $193.5117   $193.51   $193.50   $193.50  
  Purchase #6 $69.93   6.823%   $74.7013   $74.70   $74.70   $74.70  
  Purchase #7 $145.44   12.158%   $163.1226   $163.12   $163.10   $163.10  
  7 purchase totals = $1,088.24       $1,200.5884   $1,200.58   $1,200.60   $1,200.60