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 $246.34   6.829%   $263.1626   $263.16   $263.15   $263.20  
  Purchase #2 $248.37   13.753%   $282.5283   $282.53   $282.55   $282.50  
  Purchase #3 $131.70   12.186%   $147.749   $147.75   $147.75   $147.70  
  Purchase #4 $104.89   5.110%   $110.2499   $110.25   $110.25   $110.20  
  Purchase #5 $206.39   11.702%   $230.5418   $230.54   $230.55   $230.50  
  Purchase #6 $239.48   5.288%   $252.1437   $252.14   $252.15   $252.10  
  Purchase #7 $14.52   11.628%   $16.2084   $16.21   $16.20   $16.20  
  7 purchase totals = $1,191.69       $1,302.5837   $1,302.58   $1,302.60   $1,302.40