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 $51.98   13.435%   $58.9635   $58.96   $58.95   $59.00  
  Purchase #2 $214.78   7.869%   $231.681   $231.68   $231.70   $231.70  
  Purchase #3 $229.46   9.525%   $251.3161   $251.32   $251.30   $251.30  
  Purchase #4 $208.43   3.760%   $216.267   $216.27   $216.25   $216.30  
  Purchase #5 $31.35   10.543%   $34.6552   $34.66   $34.65   $34.70  
  Purchase #6 $217.96   12.184%   $244.5162   $244.52   $244.50   $244.50  
  Purchase #7 $124.95   13.675%   $142.0369   $142.04   $142.05   $142.00  
  7 purchase totals = $1,078.91       $1,179.4359   $1,179.45   $1,179.40   $1,179.50