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 $125.88   8.469%   $136.5408   $136.54   $136.55   $136.50  
  Purchase #2 $97.99   7.113%   $104.96   $104.96   $104.95   $105.00  
  Purchase #3 $52.87   12.666%   $59.5665   $59.57   $59.55   $59.60  
  Purchase #4 $86.41   9.781%   $94.8618   $94.86   $94.85   $94.90  
  Purchase #5 $250.91   8.646%   $272.6037   $272.60   $272.60   $272.60  
  Purchase #6 $109.59   10.854%   $121.4849   $121.48   $121.50   $121.50  
  Purchase #7 $249.36   7.718%   $268.6056   $268.61   $268.60   $268.60  
  7 purchase totals = $973.01       $1,058.6233   $1,058.62   $1,058.60   $1,058.70