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 $64.32   4.143%   $66.9848   $66.98   $67.00   $67.00  
  Purchase #2 $45.92   11.129%   $51.0304   $51.03   $51.05   $51.00  
  Purchase #3 $216.66   6.590%   $230.9379   $230.94   $230.95   $230.90  
  Purchase #4 $143.95   5.592%   $151.9997   $152.00   $152.00   $152.00  
  Purchase #5 $98.38   12.685%   $110.8595   $110.86   $110.85   $110.90  
  Purchase #6 $143.44   9.119%   $156.5203   $156.52   $156.50   $156.50  
  Purchase #7 $238.35   3.747%   $247.281   $247.28   $247.30   $247.30  
  7 purchase totals = $951.02       $1,015.6136   $1,015.61   $1,015.65   $1,015.60