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 $125.56   8.751%   $136.5478   $136.55   $136.55   $136.50  
  Purchase #2 $165.29   4.327%   $172.4421   $172.44   $172.45   $172.40  
  Purchase #3 $99.64   7.221%   $106.835   $106.84   $106.85   $106.80  
  Purchase #4 $207.82   7.251%   $222.889   $222.89   $222.90   $222.90  
  Purchase #5 $193.31   13.535%   $219.4745   $219.47   $219.45   $219.50  
  Purchase #6 $237.88   8.854%   $258.9419   $258.94   $258.95   $258.90  
  Purchase #7 $239.37   8.543%   $259.8194   $259.82   $259.80   $259.80  
  7 purchase totals = $1,268.87       $1,376.9497   $1,376.95   $1,376.95   $1,376.80