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 $86.47   7.622%   $93.0607   $93.06   $93.05   $93.10  
  Purchase #2 $6.41   4.487%   $6.6976   $6.70   $6.70   $6.70  
  Purchase #3 $189.70   8.653%   $206.1147   $206.11   $206.10   $206.10  
  Purchase #4 $56.28   6.638%   $60.0159   $60.02   $60.00   $60.00  
  Purchase #5 $198.58   7.674%   $213.819   $213.82   $213.80   $213.80  
  Purchase #6 $235.75   13.790%   $268.2599   $268.26   $268.25   $268.30  
  Purchase #7 $135.99   7.191%   $145.769   $145.77   $145.75   $145.80  
  7 purchase totals = $909.18       $993.7368   $993.74   $993.65   $993.80