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 $86.34   10.346%   $95.2727   $95.27   $95.25   $95.30  
  Purchase #2 $225.95   7.731%   $243.4182   $243.42   $243.40   $243.40  
  Purchase #3 $77.44   9.307%   $84.6473   $84.65   $84.65   $84.60  
  Purchase #4 $178.54   11.214%   $198.5615   $198.56   $198.55   $198.60  
  Purchase #5 $223.30   6.527%   $237.8748   $237.87   $237.85   $237.90  
  Purchase #6 $99.46   4.521%   $103.9566   $103.96   $103.95   $104.00  
  Purchase #7 $41.77   3.198%   $43.1058   $43.11   $43.10   $43.10  
  7 purchase totals = $932.80       $1,006.8369   $1,006.84   $1,006.75   $1,006.90