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 $150.45   11.603%   $167.9067   $167.91   $167.90   $167.90  
  Purchase #2 $177.61   8.846%   $193.3214   $193.32   $193.30   $193.30  
  Purchase #3 $17.51   6.828%   $18.7056   $18.71   $18.70   $18.70  
  Purchase #4 $235.62   5.848%   $249.3991   $249.40   $249.40   $249.40  
  Purchase #5 $16.59   5.616%   $17.5217   $17.52   $17.50   $17.50  
  Purchase #6 $108.84   3.829%   $113.0075   $113.01   $113.00   $113.00  
  Purchase #7 $70.32   9.620%   $77.0848   $77.08   $77.10   $77.10  
  7 purchase totals = $776.94       $836.9468   $836.95   $836.90   $836.90