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 $195.77   10.136%   $215.6132   $215.61   $215.60   $215.60  
  Purchase #2 $102.46   9.396%   $112.0871   $112.09   $112.10   $112.10  
  Purchase #3 $120.30   6.137%   $127.6828   $127.68   $127.70   $127.70  
  Purchase #4 $95.75   11.398%   $106.6636   $106.66   $106.65   $106.70  
  Purchase #5 $167.76   6.607%   $178.8439   $178.84   $178.85   $178.80  
  Purchase #6 $59.58   11.630%   $66.5092   $66.51   $66.50   $66.50  
  Purchase #7 $153.96   8.665%   $167.3006   $167.30   $167.30   $167.30  
  7 purchase totals = $895.58       $974.7004   $974.69   $974.70   $974.70