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 $59.66   10.790%   $66.0973   $66.10   $66.10   $66.10  
  Purchase #2 $237.80   7.483%   $255.5946   $255.59   $255.60   $255.60  
  Purchase #3 $51.52   8.783%   $56.045   $56.05   $56.05   $56.00  
  Purchase #4 $179.75   4.412%   $187.6806   $187.68   $187.70   $187.70  
  Purchase #5 $230.46   9.688%   $252.787   $252.79   $252.80   $252.80  
  Purchase #6 $88.66   7.187%   $95.032   $95.03   $95.05   $95.00  
  Purchase #7 $112.64   10.766%   $124.7668   $124.77   $124.75   $124.80  
  7 purchase totals = $960.49       $1,038.0033   $1,038.01   $1,038.05   $1,038.00