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 $212.30   11.121%   $235.9099   $235.91   $235.90   $235.90  
  Purchase #2 $136.45   3.416%   $141.1111   $141.11   $141.10   $141.10  
  Purchase #3 $9.54   12.867%   $10.7675   $10.77   $10.75   $10.80  
  Purchase #4 $194.44   11.870%   $217.52   $217.52   $217.50   $217.50  
  Purchase #5 $56.85   4.383%   $59.3417   $59.34   $59.35   $59.30  
  Purchase #6 $32.40   7.209%   $34.7357   $34.74   $34.75   $34.70  
  Purchase #7 $166.89   6.256%   $177.3306   $177.33   $177.35   $177.30  
  7 purchase totals = $808.87       $876.7165   $876.72   $876.70   $876.60