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 $197.62   13.394%   $224.0892   $224.09   $224.10   $224.10  
  Purchase #2 $43.93   5.512%   $46.3514   $46.35   $46.35   $46.40  
  Purchase #3 $124.48   5.525%   $131.3575   $131.36   $131.35   $131.40  
  Purchase #4 $169.76   6.525%   $180.8368   $180.84   $180.85   $180.80  
  Purchase #5 $211.52   11.306%   $235.4345   $235.43   $235.45   $235.40  
  Purchase #6 $246.89   9.153%   $269.4878   $269.49   $269.50   $269.50  
  Purchase #7 $246.84   9.739%   $270.8797   $270.88   $270.90   $270.90  
  7 purchase totals = $1,241.04       $1,358.4369   $1,358.44   $1,358.50   $1,358.50