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 $185.80   11.214%   $206.6356   $206.64   $206.65   $206.60  
  Purchase #2 $152.93   13.613%   $173.7484   $173.75   $173.75   $173.70  
  Purchase #3 $95.82   10.705%   $106.0775   $106.08   $106.10   $106.10  
  Purchase #4 $217.47   9.805%   $238.7929   $238.79   $238.80   $238.80  
  Purchase #5 $175.48   5.214%   $184.6295   $184.63   $184.65   $184.60  
  Purchase #6 $56.92   11.230%   $63.3121   $63.31   $63.30   $63.30  
  Purchase #7 $31.72   5.315%   $33.4059   $33.41   $33.40   $33.40  
  7 purchase totals = $916.14       $1,006.6019   $1,006.61   $1,006.65   $1,006.50