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 $56.27   7.333%   $60.3963   $60.40   $60.40   $60.40  
  Purchase #2 $41.82   11.301%   $46.5461   $46.55   $46.55   $46.50  
  Purchase #3 $220.71   6.689%   $235.4733   $235.47   $235.45   $235.50  
  Purchase #4 $5.91   7.317%   $6.3424   $6.34   $6.35   $6.30  
  Purchase #5 $222.61   9.348%   $243.4196   $243.42   $243.40   $243.40  
  Purchase #6 $104.39   12.740%   $117.6893   $117.69   $117.70   $117.70  
  Purchase #7 $59.29   4.454%   $61.9308   $61.93   $61.95   $61.90  
  7 purchase totals = $711.00       $771.7978   $771.80   $771.80   $771.70