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 $225.87   9.160%   $246.5597   $246.56   $246.55   $246.60  
  Purchase #2 $187.80   3.265%   $193.9317   $193.93   $193.95   $193.90  
  Purchase #3 $86.62   5.183%   $91.1095   $91.11   $91.10   $91.10  
  Purchase #4 $122.96   6.599%   $131.0741   $131.07   $131.05   $131.10  
  Purchase #5 $89.41   7.457%   $96.0773   $96.08   $96.10   $96.10  
  Purchase #6 $114.44   3.656%   $118.6239   $118.62   $118.60   $118.60  
  Purchase #7 $150.67   10.186%   $166.0172   $166.02   $166.00   $166.00  
  7 purchase totals = $977.77       $1,043.3934   $1,043.39   $1,043.35   $1,043.40