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 $142.89   10.613%   $158.0549   $158.05   $158.05   $158.10  
  Purchase #2 $53.62   8.296%   $58.0683   $58.07   $58.05   $58.10  
  Purchase #3 $149.77   11.724%   $167.329   $167.33   $167.35   $167.30  
  Purchase #4 $86.57   11.471%   $96.5004   $96.50   $96.50   $96.50  
  Purchase #5 $175.77   12.314%   $197.4143   $197.41   $197.40   $197.40  
  Purchase #6 $183.85   5.811%   $194.5335   $194.53   $194.55   $194.50  
  Purchase #7 $159.97   12.238%   $179.5471   $179.55   $179.55   $179.50  
  7 purchase totals = $952.44       $1,051.4475   $1,051.44   $1,051.45   $1,051.40