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 $37.70   10.365%   $41.6076   $41.61   $41.60   $41.60  
  Purchase #2 $191.57   5.389%   $201.8937   $201.89   $201.90   $201.90  
  Purchase #3 $249.94   9.638%   $274.0292   $274.03   $274.05   $274.00  
  Purchase #4 $72.25   13.408%   $81.9373   $81.94   $81.95   $81.90  
  Purchase #5 $56.28   13.664%   $63.9701   $63.97   $63.95   $64.00  
  Purchase #6 $29.96   6.775%   $31.9898   $31.99   $32.00   $32.00  
  Purchase #7 $82.92   10.449%   $91.5843   $91.58   $91.60   $91.60  
  7 purchase totals = $720.62       $787.0120   $787.01   $787.05   $787.00