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 $202.68   11.233%   $225.447   $225.45   $225.45   $225.40  
  Purchase #2 $189.40   3.332%   $195.7108   $195.71   $195.70   $195.70  
  Purchase #3 $33.28   4.565%   $34.7992   $34.80   $34.80   $34.80  
  Purchase #4 $182.95   9.480%   $200.2937   $200.29   $200.30   $200.30  
  Purchase #5 $200.95   11.217%   $223.4906   $223.49   $223.50   $223.50  
  Purchase #6 $228.32   5.689%   $241.3091   $241.31   $241.30   $241.30  
  Purchase #7 $201.61   10.551%   $222.8819   $222.88   $222.90   $222.90  
  7 purchase totals = $1,239.19       $1,343.9323   $1,343.93   $1,343.95   $1,343.90