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 $178.56   8.401%   $193.5608   $193.56   $193.55   $193.60  
  Purchase #2 $215.44   10.173%   $237.3567   $237.36   $237.35   $237.40  
  Purchase #3 $55.50   5.548%   $58.5791   $58.58   $58.60   $58.60  
  Purchase #4 $200.81   7.710%   $216.2925   $216.29   $216.30   $216.30  
  Purchase #5 $74.92   12.760%   $84.4798   $84.48   $84.50   $84.50  
  Purchase #6 $226.84   8.322%   $245.7176   $245.72   $245.70   $245.70  
  Purchase #7 $123.64   9.142%   $134.9432   $134.94   $134.95   $134.90  
  7 purchase totals = $1,075.71       $1,170.9297   $1,170.93   $1,170.95   $1,171.00