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 $86.54   10.412%   $95.5505   $95.55   $95.55   $95.60  
  Purchase #2 $146.67   13.517%   $166.4954   $166.50   $166.50   $166.50  
  Purchase #3 $57.61   12.481%   $64.8003   $64.80   $64.80   $64.80  
  Purchase #4 $170.73   6.259%   $181.416   $181.42   $181.40   $181.40  
  Purchase #5 $13.68   10.819%   $15.16   $15.16   $15.15   $15.20  
  Purchase #6 $49.84   7.507%   $53.5815   $53.58   $53.60   $53.60  
  Purchase #7 $232.69   11.264%   $258.9002   $258.90   $258.90   $258.90  
  7 purchase totals = $757.76       $835.9039   $835.91   $835.90   $836.00