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 $91.29   12.847%   $103.018   $103.02   $103.00   $103.00  
  Purchase #2 $60.83   9.508%   $66.6137   $66.61   $66.60   $66.60  
  Purchase #3 $51.54   5.556%   $54.4036   $54.40   $54.40   $54.40  
  Purchase #4 $114.33   12.259%   $128.3457   $128.35   $128.35   $128.30  
  Purchase #5 $245.90   9.783%   $269.9564   $269.96   $269.95   $270.00  
  Purchase #6 $228.58   13.600%   $259.6669   $259.67   $259.65   $259.70  
  Purchase #7 $187.84   7.336%   $201.6199   $201.62   $201.60   $201.60  
  7 purchase totals = $980.31       $1,083.6242   $1,083.63   $1,083.55   $1,083.60