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 $5.58   6.533%   $5.9445   $5.94   $5.95   $5.90  
  Purchase #2 $194.49   9.365%   $212.704   $212.70   $212.70   $212.70  
  Purchase #3 $208.50   9.164%   $227.6069   $227.61   $227.60   $227.60  
  Purchase #4 $122.29   4.230%   $127.4629   $127.46   $127.45   $127.50  
  Purchase #5 $165.33   8.725%   $179.755   $179.76   $179.75   $179.80  
  Purchase #6 $51.56   3.623%   $53.428   $53.43   $53.45   $53.40  
  Purchase #7 $211.93   12.809%   $239.0761   $239.08   $239.10   $239.10  
  7 purchase totals = $959.68       $1,045.9774   $1,045.98   $1,046.00   $1,046.00