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 $34.67   10.275%   $38.2323   $38.23   $38.25   $38.20  
  Purchase #2 $106.81   11.410%   $118.997   $119.00   $119.00   $119.00  
  Purchase #3 $198.63   3.620%   $205.8204   $205.82   $205.80   $205.80  
  Purchase #4 $104.94   12.300%   $117.8476   $117.85   $117.85   $117.80  
  Purchase #5 $49.32   5.287%   $51.9275   $51.93   $51.95   $51.90  
  Purchase #6 $167.77   7.138%   $179.7454   $179.75   $179.75   $179.70  
  Purchase #7 $138.79   6.403%   $147.6767   $147.68   $147.70   $147.70  
  7 purchase totals = $800.93       $860.2469   $860.26   $860.30   $860.10