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 $244.68   7.260%   $262.4438   $262.44   $262.45   $262.40  
  Purchase #2 $61.31   9.237%   $66.9732   $66.97   $66.95   $67.00  
  Purchase #3 $72.98   3.531%   $75.5569   $75.56   $75.55   $75.60  
  Purchase #4 $18.54   4.278%   $19.3331   $19.33   $19.35   $19.30  
  Purchase #5 $245.61   12.135%   $275.4148   $275.41   $275.40   $275.40  
  Purchase #6 $38.85   12.640%   $43.7606   $43.76   $43.75   $43.80  
  Purchase #7 $246.91   11.793%   $276.0281   $276.03   $276.05   $276.00  
  7 purchase totals = $928.88       $1,019.5105   $1,019.50   $1,019.50   $1,019.50