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 $49.37   5.543%   $52.1066   $52.11   $52.10   $52.10  
  Purchase #2 $246.59   9.398%   $269.7645   $269.76   $269.75   $269.80  
  Purchase #3 $175.62   4.771%   $183.9988   $184.00   $184.00   $184.00  
  Purchase #4 $80.60   11.224%   $89.6465   $89.65   $89.65   $89.60  
  Purchase #5 $118.80   4.113%   $123.6862   $123.69   $123.70   $123.70  
  Purchase #6 $119.59   7.483%   $128.5389   $128.54   $128.55   $128.50  
  Purchase #7 $98.88   3.397%   $102.239   $102.24   $102.25   $102.20  
  7 purchase totals = $889.45       $949.9805   $949.99   $950.00   $949.90