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 $97.33   8.116%   $105.2293   $105.23   $105.25   $105.20  
  Purchase #2 $155.57   3.194%   $160.5389   $160.54   $160.55   $160.50  
  Purchase #3 $170.58   13.544%   $193.6834   $193.68   $193.70   $193.70  
  Purchase #4 $241.30   5.203%   $253.8548   $253.85   $253.85   $253.90  
  Purchase #5 $46.50   3.501%   $48.128   $48.13   $48.15   $48.10  
  Purchase #6 $106.52   8.790%   $115.8831   $115.88   $115.90   $115.90  
  Purchase #7 $131.93   13.375%   $149.5756   $149.58   $149.60   $149.60  
  7 purchase totals = $949.73       $1,026.8931   $1,026.89   $1,027.00   $1,026.90