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 $20.56   9.385%   $22.4896   $22.49   $22.50   $22.50  
  Purchase #2 $107.40   7.632%   $115.5968   $115.60   $115.60   $115.60  
  Purchase #3 $224.31   3.200%   $231.4879   $231.49   $231.50   $231.50  
  Purchase #4 $178.51   12.822%   $201.3986   $201.40   $201.40   $201.40  
  Purchase #5 $232.60   3.699%   $241.2039   $241.20   $241.20   $241.20  
  Purchase #6 $41.75   7.757%   $44.9885   $44.99   $45.00   $45.00  
  Purchase #7 $244.40   5.815%   $258.6119   $258.61   $258.60   $258.60  
  7 purchase totals = $1,049.53       $1,115.7772   $1,115.78   $1,115.80   $1,115.80