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 $116.28   9.282%   $127.0731   $127.07   $127.05   $127.10  
  Purchase #2 $157.90   11.845%   $176.6033   $176.60   $176.60   $176.60  
  Purchase #3 $124.55   11.258%   $138.5718   $138.57   $138.55   $138.60  
  Purchase #4 $84.98   3.564%   $88.0087   $88.01   $88.00   $88.00  
  Purchase #5 $23.72   5.706%   $25.0735   $25.07   $25.05   $25.10  
  Purchase #6 $181.61   11.494%   $202.4843   $202.48   $202.50   $202.50  
  Purchase #7 $230.91   4.406%   $241.0839   $241.08   $241.10   $241.10  
  7 purchase totals = $919.95       $998.8986   $998.88   $998.85   $999.00