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 $53.91   11.668%   $60.2002   $60.20   $60.20   $60.20  
  Purchase #2 $67.72   6.166%   $71.8956   $71.90   $71.90   $71.90  
  Purchase #3 $205.87   9.118%   $224.6412   $224.64   $224.65   $224.60  
  Purchase #4 $164.52   7.581%   $176.9923   $176.99   $177.00   $177.00  
  Purchase #5 $210.80   12.661%   $237.4894   $237.49   $237.50   $237.50  
  Purchase #6 $243.42   3.754%   $252.558   $252.56   $252.55   $252.60  
  Purchase #7 $186.27   9.447%   $203.8669   $203.87   $203.85   $203.90  
  7 purchase totals = $1,132.51       $1,227.6436   $1,227.65   $1,227.65   $1,227.70