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 $241.57   11.501%   $269.353   $269.35   $269.35   $269.40  
  Purchase #2 $86.75   11.690%   $96.8911   $96.89   $96.90   $96.90  
  Purchase #3 $120.41   13.495%   $136.6593   $136.66   $136.65   $136.70  
  Purchase #4 $140.53   3.631%   $145.6326   $145.63   $145.65   $145.60  
  Purchase #5 $53.80   13.140%   $60.8693   $60.87   $60.85   $60.90  
  Purchase #6 $192.92   9.577%   $211.3959   $211.40   $211.40   $211.40  
  Purchase #7 $44.30   6.319%   $47.0993   $47.10   $47.10   $47.10  
  7 purchase totals = $880.28       $967.9005   $967.90   $967.90   $968.00