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 $64.74   13.468%   $73.4592   $73.46   $73.45   $73.50  
  Purchase #2 $163.69   7.319%   $175.6705   $175.67   $175.65   $175.70  
  Purchase #3 $120.32   3.699%   $124.7706   $124.77   $124.75   $124.80  
  Purchase #4 $226.36   4.191%   $235.8467   $235.85   $235.85   $235.80  
  Purchase #5 $44.91   3.146%   $46.3229   $46.32   $46.30   $46.30  
  Purchase #6 $163.46   9.268%   $178.6095   $178.61   $178.60   $178.60  
  Purchase #7 $147.52   6.412%   $156.979   $156.98   $157.00   $157.00  
  7 purchase totals = $931.00       $991.6584   $991.66   $991.60   $991.70