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 $54.86   11.128%   $60.9648   $60.96   $60.95   $61.00  
  Purchase #2 $224.28   6.229%   $238.2504   $238.25   $238.25   $238.30  
  Purchase #3 $179.78   12.103%   $201.5388   $201.54   $201.55   $201.50  
  Purchase #4 $247.26   10.809%   $273.9863   $273.99   $274.00   $274.00  
  Purchase #5 $36.39   9.283%   $39.7681   $39.77   $39.75   $39.80  
  Purchase #6 $182.60   4.821%   $191.4031   $191.40   $191.40   $191.40  
  Purchase #7 $85.68   9.195%   $93.5583   $93.56   $93.55   $93.60  
  7 purchase totals = $1,010.85       $1,099.4698   $1,099.47   $1,099.45   $1,099.60