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 $95.86   3.209%   $98.9361   $98.94   $98.95   $98.90  
  Purchase #2 $137.80   9.142%   $150.3977   $150.40   $150.40   $150.40  
  Purchase #3 $121.82   13.269%   $137.9843   $137.98   $138.00   $138.00  
  Purchase #4 $96.65   5.822%   $102.277   $102.28   $102.30   $102.30  
  Purchase #5 $172.54   12.129%   $193.4674   $193.47   $193.45   $193.50  
  Purchase #6 $152.98   6.840%   $163.4438   $163.44   $163.45   $163.40  
  Purchase #7 $184.26   7.868%   $198.7576   $198.76   $198.75   $198.80  
  7 purchase totals = $961.91       $1,045.2639   $1,045.27   $1,045.30   $1,045.30