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 $63.59   3.852%   $66.0395   $66.04   $66.05   $66.00  
  Purchase #2 $165.34   11.279%   $183.9887   $183.99   $184.00   $184.00  
  Purchase #3 $228.99   6.429%   $243.7118   $243.71   $243.70   $243.70  
  Purchase #4 $32.30   7.553%   $34.7396   $34.74   $34.75   $34.70  
  Purchase #5 $18.27   6.413%   $19.4417   $19.44   $19.45   $19.40  
  Purchase #6 $205.96   7.174%   $220.7356   $220.74   $220.75   $220.70  
  Purchase #7 $235.33   5.541%   $248.3696   $248.37   $248.35   $248.40  
  7 purchase totals = $949.78       $1,017.0265   $1,017.03   $1,017.05   $1,016.90