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 $66.52   3.819%   $69.0604   $69.06   $69.05   $69.10  
  Purchase #2 $49.98   7.131%   $53.5441   $53.54   $53.55   $53.50  
  Purchase #3 $183.73   7.288%   $197.1202   $197.12   $197.10   $197.10  
  Purchase #4 $48.26   8.664%   $52.4412   $52.44   $52.45   $52.40  
  Purchase #5 $134.65   9.617%   $147.5993   $147.60   $147.60   $147.60  
  Purchase #6 $167.99   11.790%   $187.796   $187.80   $187.80   $187.80  
  Purchase #7 $13.25   13.188%   $14.9974   $15.00   $15.00   $15.00  
  7 purchase totals = $664.38       $722.5586   $722.56   $722.55   $722.50