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 $216.87   5.112%   $227.9564   $227.96   $227.95   $228.00  
  Purchase #2 $230.40   8.778%   $250.6245   $250.62   $250.60   $250.60  
  Purchase #3 $201.92   5.546%   $213.1185   $213.12   $213.10   $213.10  
  Purchase #4 $54.44   9.433%   $59.5753   $59.58   $59.60   $59.60  
  Purchase #5 $34.93   8.759%   $37.9895   $37.99   $38.00   $38.00  
  Purchase #6 $13.78   6.288%   $14.6465   $14.65   $14.65   $14.60  
  Purchase #7 $183.87   6.779%   $196.3345   $196.33   $196.35   $196.30  
  7 purchase totals = $936.21       $1,000.2452   $1,000.25   $1,000.25   $1,000.20