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 $61.75   12.213%   $69.2915   $69.29   $69.30   $69.30  
  Purchase #2 $35.46   4.117%   $36.9199   $36.92   $36.90   $36.90  
  Purchase #3 $171.45   6.464%   $182.5325   $182.53   $182.55   $182.50  
  Purchase #4 $48.66   13.208%   $55.087   $55.09   $55.10   $55.10  
  Purchase #5 $225.41   11.816%   $252.0444   $252.04   $252.05   $252.00  
  Purchase #6 $141.47   5.603%   $149.3966   $149.40   $149.40   $149.40  
  Purchase #7 $103.54   9.638%   $113.5192   $113.52   $113.50   $113.50  
  7 purchase totals = $787.74       $858.7911   $858.79   $858.80   $858.70