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 $130.53   11.676%   $145.7707   $145.77   $145.75   $145.80  
  Purchase #2 $53.57   5.157%   $56.3326   $56.33   $56.35   $56.30  
  Purchase #3 $27.85   7.567%   $29.9574   $29.96   $29.95   $30.00  
  Purchase #4 $175.81   9.632%   $192.744   $192.74   $192.75   $192.70  
  Purchase #5 $129.31   6.167%   $137.2845   $137.28   $137.30   $137.30  
  Purchase #6 $249.81   6.669%   $266.4698   $266.47   $266.45   $266.50  
  Purchase #7 $125.76   6.121%   $133.4578   $133.46   $133.45   $133.50  
  7 purchase totals = $892.64       $962.0168   $962.01   $962.00   $962.10