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 $58.32   5.197%   $61.3509   $61.35   $61.35   $61.40  
  Purchase #2 $86.84   6.466%   $92.4551   $92.46   $92.45   $92.50  
  Purchase #3 $216.69   6.853%   $231.5398   $231.54   $231.55   $231.50  
  Purchase #4 $207.96   13.394%   $235.8142   $235.81   $235.80   $235.80  
  Purchase #5 $219.86   4.150%   $228.9842   $228.98   $229.00   $229.00  
  Purchase #6 $44.43   11.709%   $49.6323   $49.63   $49.65   $49.60  
  Purchase #7 $157.51   8.699%   $171.2118   $171.21   $171.20   $171.20  
  7 purchase totals = $991.61       $1,070.9883   $1,070.98   $1,071.00   $1,071.00