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 $250.98   7.511%   $269.8311   $269.83   $269.85   $269.80  
  Purchase #2 $117.41   8.299%   $127.1539   $127.15   $127.15   $127.20  
  Purchase #3 $59.70   3.220%   $61.6223   $61.62   $61.60   $61.60  
  Purchase #4 $104.90   13.399%   $118.9556   $118.96   $118.95   $119.00  
  Purchase #5 $194.76   3.270%   $201.1287   $201.13   $201.15   $201.10  
  Purchase #6 $147.44   5.645%   $155.763   $155.76   $155.75   $155.80  
  Purchase #7 $101.85   3.563%   $105.4789   $105.48   $105.50   $105.50  
  7 purchase totals = $977.04       $1,039.9335   $1,039.93   $1,039.95   $1,040.00