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 $200.41   12.745%   $225.9523   $225.95   $225.95   $226.00  
  Purchase #2 $15.67   5.847%   $16.5862   $16.59   $16.60   $16.60  
  Purchase #3 $135.98   8.458%   $147.4812   $147.48   $147.50   $147.50  
  Purchase #4 $220.40   11.276%   $245.2523   $245.25   $245.25   $245.30  
  Purchase #5 $104.79   6.745%   $111.8581   $111.86   $111.85   $111.90  
  Purchase #6 $236.32   5.819%   $250.0715   $250.07   $250.05   $250.10  
  Purchase #7 $50.60   8.669%   $54.9865   $54.99   $55.00   $55.00  
  7 purchase totals = $964.17       $1,052.1881   $1,052.19   $1,052.20   $1,052.40