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 $240.38   9.595%   $263.4445   $263.44   $263.45   $263.40  
  Purchase #2 $39.79   9.816%   $43.6958   $43.70   $43.70   $43.70  
  Purchase #3 $26.60   6.856%   $28.4237   $28.42   $28.40   $28.40  
  Purchase #4 $118.41   4.132%   $123.3027   $123.30   $123.30   $123.30  
  Purchase #5 $244.88   13.843%   $278.7787   $278.78   $278.80   $278.80  
  Purchase #6 $23.74   4.405%   $24.7857   $24.79   $24.80   $24.80  
  Purchase #7 $51.89   3.743%   $53.8322   $53.83   $53.85   $53.80  
  7 purchase totals = $745.69       $816.2633   $816.26   $816.30   $816.20